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Foundations in Molecular Biology and Genetics: Midterm
University of Guelph MBG*2040
574
Microbiology
Undergraduate 2
10/30/2015

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Cards

Term
3' end
Definition
The  end of one of the strands in a DNA molecule, ending with C3 of the pentose sugar.
Term
5' end
Definition
The end of one of the strands in a DNA  molecule, ending with C5 on the pentose sugar.
Term
1000 Genomes Project
Definition
Launched in 2008. Sequencing at least 2500 genomes from people all over the world, from different ancestral groups. Provides detailed information about human genetic diversity. Different people have high variation in copy number of repetitive DNA sequences: used in DNA fingerprinting, forensics, and paternity testing.
Term
ABO blood types
Definition
An example of codominance. There are three alleles: IA, IB, and i, which code for acetylgalactosamine, galactose, and nothing, respectively, on the surface of red blood cells. Linked to Nail-Patella syndrome.
Term
Acentric fragment
Definition
A chromosome fragment lacking a centromere. It is unable to move into place during anaphase, so it is lost.
Term
Acetylgalactosamine
Definition
Present on the surface of red blood cells of individuals with an IA allele: type A and type AB blood.
Term
Acrocentric chromosome
Definition
A chromosome with the centromere near the ends of the chromatids.
Term
Adenine (A)
Definition
A nitrogen-containing base found in DNA and RNA. A purine with two rings, and one NH2 group. Pairs with thymine or uracil, forming two hydrogen bonds. Its nucleotide is dAMP.
Term
Adjacent disjunction I
Definition
One of the three possible disjunction evens from a cruciform pairing in a translocation heterozygote. Centromeres that move to the same pole are from heterologous chromosomes: one euploid chromatid and one translocated chromatid to each pole. Only aneuploid gametes are produced.
Term
Adjacent disjunction II
Definition
One of the three possible disjunction events from a cruciform pairing in a translocation heterozygote. Centromeres that move to the same pole are from homologous chromosomes: one euploid chromatid and one translocated chromatid to each pole. Only aneuploid gametes are produced.
Term
Agglutination
Definition
The reaction between antigens in blood and their specific serum. Used to detect blood type.
Term
Albert Blakeslee and John Belling
Definition
Studied aneuploidies in Datura stramonium.
Term
Albinism
Definition

"Colourless"

A recessive condition resulting from a null allele. Proteins necessary for producing melanin, a dark pigment, are absent.

Term
Alexander Fleming
Definition
Discovered penicillin.
Term
Alfred H. Sturtevant
Definition
An undergraduate working in the lab of T.H. Morgan. Created the first chromosome map using experimental data. Based his mapping principle on the principle that genes on the same chromosome are linked.
Term
Allele
Definition
Different forms of a gene, which may display different phenotypes. Some genes have many alleles. Some alleles are associated with certain breeds or varieties. Frequencies of alleles varies form population to population.
Term
Allelic series
Definition

aka Dominance series

An arrangement of multiple alleles by order of dominance. Equal signs signify incomplete dominance or codominance. Describes the hierarchy of multiple alleles. Null alleles are often the most recessive. Hypomorphic alleles are often in the middle. Wild type alleles are often the most dominant.

Term
Allopolyploid
Definition

"Other"

Polyploids formed by hybridization between different species. More likely to be fertile than autopolyploids because the two sets of chromosomes are dissimilar and more likely to pair regularly. 

Term
Alternate disjunction
Definition
One of the three possible disjunction events from a cruciform pairing in a translocation heterozygote. All euploid chromatids move to one pole, and all translcoated chromatids move to the other. Produces only euploid gametes: half with euploid chromatids, and half with translocated chromatids. The only disjunction event that produces viable gametes.
Term
American cotton
Definition

2n = 26

Originated in Peru. Crossed with Old World cotton to produce upland cotton.

Term
Amino acid
Definition
The building block of polypeptides. There are 20 different amino acids, which are either synthesized or obtained form the diet. A central carbon atom to which an amino group, a carboxyl group, a hydrogen atom, and a side group are attached. In polypeptides, a peptide bond forms between the amino group and the carboxyl group of another amino acid.
Term
Amino group (NH2)
Definition
A component of an amino acid. Attached to the central carbon. It forms peptide bonds with carboxyl groups from other amino acids.
Term
Aminocentesis
Definition
A small amount of amniotic fluid is removed from the amniotic sac by inserting a needly into the abdomen of a pregnant woman. Fetal cells can be found in the fluid, and may be tested for genetic abnormalities in the fetus. The test may take up to 3 weeks.
Term
Amphidiploid
Definition
A fertile allotetraploid. Amphidiploids are fertile because the two of the four sets of chromosomes are similar enough to each other that they pair regularly, such as in allopolyploids. Example: upland cotton.
Term
Anaphase
Definition
The fourth stage of mitosis. Sister chromatids separate and become the new daughter chromosomes that are pulled to each pole. The separate copies of DNA are separated.
Term
Anaphase I
Definition
The third phase of meiosis I. Homologs move toward their poles, guided by microtubules. Cytokinesis and division of the cytoplasm begins; a cleavage furrow becomes prominent.
Term
Anaphase II
Definition
The third phase of meiosis II. Sister chromatids separate and become daughter chromosomes, which are pulled to each pole by kinetochore microtubules. The arms of the daugher chromosome lag behind. Completes the separation of identical copies of DNA that was replicated in interphase. Identical to anaphase of mitosis.
Term
André Lwoff
Definition
Discovered bacteriophage lambda in 1965. Won the Nobel Prize in Physiology or Medicine.
Term
Aneuploid
Definition

"Not good fold"

One chromosome or chromosome segment is over or under-represented. Creates a genetic imbalance that produces a phenotypic effect. Hypopoloid or hyperploid.

Term
Antennapedia (Antp)
Definition
A gain-of-function mutation in Drosophila. Causes proteins for legs to be produced in the antennae, resulting in legs growing from the head instead of antennae.
Term
Anthocyanin
Definition
A purple pigment produced in purple flowers.
Term
Antibiotics
Definition
A group of drugs which kills bacteria. Includes ampicillin, kanamycin, tetracyclin, streptomycin, sulfanilamide, and chloramphenicol. Use of antibiotics increased after streptomycin was discovered in 1943, and soon bacteria evolved genes that made them resistant to antibiotics. Bacteria are evolving due to over-use of antibiotics: they are often prescribed for viral infections, found in hand soaps, and used in animal feed. Denmark and Sweden have bans on non-therapeutic use of antibiotics in animals.
Term
Anticodons
Definition
Components of tRNA. Recognize their complementary codon in mRNA.
Term
Apomixis
Definition
A form of asexual reproduction in plants, where an unreduced egg forms a seed without meiosis or fertilization.
Term
Attached-X chromosome
Definition
Compound chromosomes in Drosophila, resultant of the fusion of two X chromosomes. Discovered by Lillian Morgan. Females with X-linked mutations were crossed with wild-type males, producing unusual progeny ratios.
Term
Autonomous state
Definition
A type of F factor. Replicates independently from the bacterial chromosome. Cells with autonomous F factors are F+ cells. Integration of the F factor into the recipient cell is mediated by DNA sequences on the F factor as well as on the chromosome.
Term
Autopolyploid
Definition

"Self"

Polyploids created by crossing within one species. A single genome is muliplied to create extra sets of chromosomes. In plants there is more vegetative growth: larger cells, thicker laves, bigger flowers, larger plants, bigger fruits, less seed production.

Term
Autosome
Definition
Non-sex chromosomes. Present in the same number in males and females. The number and morphology varies with speices. Humans have 22 pairs of autosomes.
Term
Auxotroph
Definition
A mutant E. coli bacteria that cannot grow without the presence of a specific metabolite. Requires auxiliary nutrients.
Term
Bacillus subtilis
Definition
A bacteria which displays transformation. Will take up DNA from any source.
Term
Bacteria
Definition
The first organisms in which DNA was studied. Can be harmful diseases like tuberculosis, or helpful such as those used to make yogurt. Important in the Earth's ecosystems: erode rock, capture energy, fix nitrogen, break down dead organisms, and enable larger organisms to survive. Small, reproduce quickly, and form large colonies in just days. Can grow 1010 bacteria in a small culture tube. Can be grown on biochemically defined culture media, allowing for experiments in metabolism and drugs. Grow on liquid medium or semisolid medium with agar. Simple structure and physiology. Have diversity and heritable phenotypes. The tenomes of many bacteria are sequenced. They have a singular, circular chromosome with a few thousand genes, as well as plasmids and episomes. Reproduce by fission. Monploid, but may have more than one copy of each single chromosome. Does not have mitosis or meiosis.
Term
Bacteriophage
Definition

"Eat bacteria"

aka Bacterial virus

Inject DNA into a bacterium so that it will produce progeny phages. Virulent or temperate. Includes bacteriophages T4 and lambda.

Term
Bacteriophage T4
Definition
A bacteriophage that attacks E. coli. Consists of a DNA strand inside a protein head. Has about 168,800 base pairs, 150 genes, and 150 non-coding sequences. The central hollow core provides a channel through which DNA is injected into the bacterium. The tail sheath contracts and pushes the tail core through the bacterial cell wall. Tail fibres are used to locate receptors on theo host cell and tail pins on the base plate attach to receptors. All these components must function correctly for the phage to reproduce. A virulent bacterophage: enters a lytic cycle. Has ts mutants.
Term
Bacteriophage lambda (λ)
Definition
A bacteriophage that attacks E. coli. Discovered by André Lwoff. Smaller than bacteriophage T4. Has about 49,000 base pairs, and 50 genes. A temperate bacteriophage: either enters lytic cycle or lysogenic pathway. The sites where recombination occurs to integrate viral DNA with bacterial DNA are attP on the viral DNA and attB on the bacterial DNA: regions where 15 nucleotides are the same. It can act as a transducing phage with specialized transduction taking gal or bio genes.
Term
Balancer
Definition
An inverted chromosome with a dominant mutation: can be tracked through crosses without cytological examination.
Term
Bar eye mutations
Definition
In Drosophila it is associated with tandem duplication. A dominant, X-linked mutation alters the size and shape of eyes into narrow bars. Calvin Bridges found that the mutation is in the 16A region: tandem duplication causes bar eyes, and tandem triplication causes double-bar eye.
Term
Barr body
Definition
A condensed, darkly staining structure which is the inactivated X chromosome in female placental mammals. Named after Murray Barr and Ewart Mertram who discovered it in 1949. Susumu Ohno proposed that the mass was the X chromosome in 1960.
Term
Bisphenol A (BPA)
Definition
A chemical which can cause nondisjunction events. Found in plastics, especially when heated.
Term
Bivalent
Definition
Two homologous chromosomes joined together for mitosis or meiosis.
Term
Bracon hebetor
Definition
A species where males are homozygous for a sex-determining locus where females are heterozygous. There are many alleles for this locus. Crosses between unrelated individuals almost always produces females.
Term
Bread wheat
Definition

Triticum aestevium

6n = 42

A hexaploid formed from two formations of allopolyploids: the first cross between wild einkorn and wild barley, producing emmer wheat, the second cross between emmer wheat and Triticum tauschii. This produced a 3n = 21 individual, and the chromosomes were doubled. There are many varieties, including: hard red spring wheat, hard red winter wheat, soft red winter wheat, hard white wheat, and soft white wheat.

Term
Bruce Lahn and David Page
Definition
Studied 19 genes on human sex chromosomes. Found that the X and Y chromosomes share genes in different positions. At some point in evolution, inversions must have rearranged the genes relative to one another. Concluded that the X and Y chromosomes in mammals must have emerged around 240 to 320 million years ago. For humans, three additional inversions occurred between 30 and 50 billion years ago.
Term
Bursa bursa-poastoris
Definition
A plant which shows epistasis in seed capsule shape. Seed capsules are triangular unless the plant is homozygous recessive for both genes A and B, in which case they are ovoid. Both genes produce a polypeptide that can produce the triangular seed pod. A dihybrid cross produces a 15 triangular : 1 ovoid ratio.
Term
C.E. McClung, N.M. Stevens, W.S. Sutton, and E.B. Wilson
Definition
The group of American cytologists who discovered the sex chromosomes.
Term
Calvin B. Bridges
Definition
Proved the hypothesis of T.H. Morgan that the white eye mutation in Drosophila was on the sex chromosome. Performed Morgan's experiments on a larger scale, and discovered some exceptional flies, and investigated the effects of chromosome nondisjunction. Studied polytenes and Bar eye mutation in Drosophila.
Term
Calvin B. Bridges and T.M. Olbrycht
Definition
Crossed wild-type Drosophila males to females homozygous for seven recessive X-linked genes. Studied the recombination frequencies to determine the order of these genes on the chromosome map.
Term
Cancer
Definition
When normal control of cell division is absent or malfunctioning. Uncontrollable cell growth occurs.
Term
Carbohydrate
Definition
A biological macromolecule.
Term
Carboxyl group (COOH)
Definition
A component of an amino acid. Attaches to the central carbon. It forms peptide bonds with the amino groups of other amino acids.
Term
Cell cycle
Definition
The process of cell duplication. Occurs during reproduction, growth, and repair. Has three phases: mitosis, cytokinesis, and interphase.
Term
Cell division
Definition
The process by which cells duplicate their contents and then divide in two. Occurs constantly in our bodies. Involves making a copy of the cell's DNA and separating the two copies so each daughter cell has a complete set.
Term
CentiMorgan (cM)
Definition
The unit used on genetic maps. The recombination frequency x 100.
Term
Central Dogma
Definition
DNA transcribes into RNA. RNA translates into proteins.
Term
Centromere
Definition
Visible constrictions near the centre of a chromosome. Holds sister chromatids together.
Term
Charles Cotterman
Definition
In the 1940s showed that the inbreeding coefficient is the same as the probability by descent.
Term
Chemical catalyst
Definition
One of the functions of proteins. Enzymes catalyze chemical reactions. Includes pepsin.
Term
Chiasma
Definition

Plural, chiasmata

"Cross"

Points where non-sister chromatids crossover, producing recombination. Vestigal evidence of DNA exchange: entanglements created by earlier crossover events. Prevents chromatids from separating too soon, minimizing nondisjunction.

Term
Chorionic biopsy
Definition
A tube is passed into the uterus through the cervix of a pregnant woman, guided by ultrasound, to collect small amounts of chorion fetal membrane villi. The sample is tested for genetic abnormalities in fetal cells. The test may be performed earlier than amniocentesis, but is not as reliable, and increases the chances of miscarriage.
Term
Chromatid
Definition
Components of chromosomes. Identical chromatids are sister chromatids.
Term
Chromatin
Definition
Found in the nucleus. Consists on non-histone chromosomal proteins, histones, DNA, and RNA. Extent of compaction changes during cell cycle, and when genes are transcribed into RNA. After DNA replication, it becomes condesnsed into chromosomes. Includes euchromatin and heterochromatin.
Term
Chromatin fibre
Definition
A tightly wound strand of DNA with histones, 30 nm thick. There are two possible models for how the DNA packs into chromatin fibres: zigzag and solenoid. Which one is found in vivo is unknown. Chromatin fibres can stretch and contract if histone structures are changed.
Term
Chromosome
Definition
A strand of DNA. Has a centromere. Includes autosomes and sex chromosomes. Composed of chromatin.
Term
Chromosome map
Definition
Represents the linear arrangement of genes along a chromosome. Includes the genetic, physical, and genomic maps.
Term
Chromosome painting
Definition
A method of making karyotypes. An isolated DNA fragment, the probe, si dyed with a fluorescent dye, and it binds to the complementary sequence. This method pinpoints the location of the gene on the chromosome.
Term
Chromosome rearrangements
Definition
When a chromosome has a structural change. May be assocated with aneuploidy, and involved in the predisposition of certain types of cancers. Inversions and translocations. Disrupt crossing over and decreases recombination frequencies.
Term
Chromosome Theory of Heredity
Definition
Genes are on chromosomes. This was proven when Calvin Bridges proved T.H. Morgan's theory that an eye colour mutation in Drosophila was on the X chromosome. Proved further by Bridge's studies in nondisjunction in Drosophila.
Term
Clearance
Definition

aka Plaque

A visible accumulation of bacteriophages that can form on bacterial cultures within hours of infection.

Term
Cleavage furrow
Definition
Forms in late anaphase, early telophase of mitosis. Formed by actin and myosin microfilaments of the contractile ring.
Term
Clones
Definition
Genetically identical cells or individuals. Cells produced by mitosis are clones.
Term
Codominance
Definition
When a heterozygote shows phenotypes for both alleles at once. Example: human blood types.
Term
Codon
Definition
A three-nucleotide sequence on mRNA that codes for specific amino acids. Recognized by their complementary anticodons on tRNA during translation.
Term
Coefficient of coincidnce (c)
Definition
The ratio of the observed frequency of double crossovers to the expected frequency. Measures interference.
Term
Coefficient of relationship
Definition
A measure of the genetic similarity between related individuals. The inbreeding coefficient (should those individuals mate), multiplied by 2.
Term
Col plasmid
Definition

Colicinogenic factor

A plasmid which encodes proteins that kill sensitive E. coli cells. Some enable conjugation.

Term
Colchicine
Definition
A chemical which can cause nondisjunction.
Term
Collagen
Definition
A structure protein. Two or three polypeptides wrapped around each other. A fibrous protein. 40% of all protein in the body is collagen. Provides tissues with strength and flexibility. Collagen injections can be used to fight aging.
Term
Colony
Definition
A visible group of clonal bacteria.
Term
Colour blindness
Definition
Colour perception is controlle by three proteins: one for blue, green, and red light. The genes for red and green are X-linked. The gene for blue is on an autosome. Colour blindness is a faulty perception of red and green light, caused by a recessive X-linked mutation. 5% - 10% of male humans have colour blindness.
Term
Common ancestor
Definition
In inbred individuals, the ancestor(s) which is/are related to them from both the mother's and father's side.
Term
Complementation test
Definition
A method for detecting heterogeneous traits. Crossing two mutants with the same phenotype to see if the mutations are on the same gene. If offpspring show the wild-type phenotype, then the mutations are on separate genes. This only works if the mutation is recessive. A 9:7 ratio is observed from an F2 dihybrid cross.
Term
Complete dominance
Definition

aka Complete recessiveness

AA and Aa have one phenotype, and aa has another. A 3:1 ratio is observed from a monohybrid cross. A 9:3:3:1 ratio is observed from a dihybrid cross.

Term
Complete expressivity
Definition
Identical known genotypes have no variation in phenotype.
Term
Complete penetrance
Definition
Identical known genotypes all produce the expected phenotype.
Term
Cometence (Com) proteins
Definition
Proteins which enable competence in bacteria.
Term
Competent
Definition
Bacteria which can take up DNA from the environment in transformation. Have competence proteins.
Term
Compound chromosome
Definition
A chromosome resultant from a fusion of segments of homologous chromosomes. Two sister chromatids become attached and form a single genetic unit. May exists stably in a cell as long as it has one functional centromere; two functional centromeres would result in the chromosome being torn apart in mitosis. First discovered by Lillian Morgan in attached-X chromosomes in Drosophila. Includes isochromosomes.
Term
Conjugation
Definition
A parasexual process. Discoverd by Joshua Lederberg and Edward Tatum. Requires cell contact. Not sensitive to DNase. Direct transfer of DNA from one bacterium to another through the conjugation channel. The donor cell has an F factor. Transfer is initiated at oriT, and replication is rolling-circle replication. Timing of conjugation was studied by Eli Wollman and François Jacob. In E. coli conjugation starts at about 8 minutes, and takes about 100 minutesto transfer the full chromosome. Replication occurs in either direction, and all genes are replicated in order, at a constant rate. Timing of gene transfer can be used to map the chromosome.
Term
Conjugation channel
Definition
A specialized cytoplasmic bridge that forms between two bacteria for conjugation, through which DNA is passed.
Term
Consanguineous mating
Definition

"Of the same blood"

Matings between relatives. Rare in humans, depending on cultural traditions.

Term
Contractile ring
Definition
A ring that forms at the cell's equator during telophase. A prelude to cytokinesis. Has actin and myosin microfilaments that form the cleavage furrow. Pinches the cell in two by pulling the plasma membrane inward, dividing the cytoplasm.
Term
Coupling
Definition

aka Cis configuration

"Same side"

AB/ab

A linkage phase. Both dominant alleles are inherited from one parent, and both recessive alleles are inherited from the other parent.

Term
Creutzfeldt-Jakob disease
Definition
Mad Cow Disease when it infects humans.
Term
Cri-du-chat syndrome
Definition

46, del(5)(p14)

"Cry of the cat"

A deletion in chromosome 5 on the short arm. Severe mental and physical impairment with a plaintive, cat-like cry during infancy.

Term
Crossing-over
Definition
Genetic exchange between non-sister chromatids during prophase I of meiosis. Creates genetically unique chromosomes. Occurs at the chiasma. A tetrad forms and two chromatids have crossing-over. Pieces break at the site of crossover and reattach at the other chromosome. Produces two recombinant chromatids and two non-recombinant chromatids, however non-recombinant chromatids may cross-over at other loci. A single chromosome may have up to 4 separate exchanges. Cross-overs may occur between sister chromatids, producing no change. During this time, a small amount of DNA synthesis occurs: repair of broken chromatids. When there are two cross-overs they may cancel each other out. Some zones of a chromosome are more prone to cross-over than others; these areas seem more condensed on a genetic map. Cross-overs are less likely to occur near the ends of a chromosome.
Term
Cruciform pairing
Definition
The pairing pattern that is diagnostic of a translocation heterozygote. Two homologous centromeres are involved, one euploid chromatid and one translocated chromosome to each. There are three possible disjunction events: adjacent disjunction I, adjacent disjunction II, and alternate disjunction.
Term
Cystic fibrosis
Definition
A disorder which shows pleiotropy. Causes mucous to clog the lungs, leading to infections, and mucous to clog the pancreatic duct, creating digestion problems.
Term
Cytogenetic mapping
Definition

aka Physical mapping

A type of chromosome map. Mapping of genes using markers and banding on chromosomes. Done by analyzing deletions and duplications on different loci in a heterozygote. Thoroughly developed in Drosophila dueto studies in polytenes. Includes deletion and duplication mapping.

Term
Cytogenetics
Definition
The analysis of stained chromosomes. Began in the nineteengh century when European biologists discovered the behaviour of chromosomes during mitosis, meiosis, and fertilization. It blossomed with development of microscopes, preparation techniques, and stains. Still used today to diagnose chromosome abnormalities. Cell are cultured and treated with a hhypotonic solution that causes them to swell with water, spreading chromosomes to make them more visible.
Term
Cytokinesis
Definition
One of the phases of cell cycle. The division of the  cytoplasm. IN animal cells, a cleavage furrow forms. The Golgi apparatus contributes vesicles containing cell wall matric molecules that aggregate at the equator, organized by spindle apparatus.
Term
Cytosine (C)
Definition
A nitrogen-containing base found in DNA and RNA. A pyrimidine: single ring with one =O group. Pairs with guanine, forming three hydrogen bonds.
Term
dAMP
Definition

Deoxyadenosine monophosphate

The nucleotide of adenine.

Term
Daturastramonium
Definition

Jimson weed

It has 12 pairs of chromosomes, and 12 different trisomies. Albert Blakeslee and JohnBelling studied aneuploidies in this plant.

Term
Daughter cell
Definition
The two cells produced in cell division.
Term
dCMP
Definition

Deoxycytidine monophosphate

The nucleotide of cytosine.

Term
Defense
Definition
One of the functions of proteins. Antibodies attack viruses and bacteria.
Term
Deletion
Definition

aka Deficiency

Hypoploidy with a missing chromosome segment. Causes a phenotypic effect. Large deletions can be studied cytologically. In Drosophila, deletions can be studied in polytenes. Incldues Cri-du-chat syndrome.

Term
Deletion mapping
Definition
A form of cytogenetic mapping. A deletion uncovers a recessive mutation, localizing a gene within the boundaries of the deletion.
Term
Denaturation
Definition
Heating DNA to near 100°C, causing hydrogen bonds to break and the strands to separate.
Term
Deoxyribose
Definition
The pentose sugar found in the nucleotides of DNA.
Term
dGMP
Definition

Deoxyguanosine monophosphate

The nucleoside of guanine.

Term
Dicentric chromatid bridge
Definition
A chromosome fragment with two centromeres. The chromatid breaks into pieces as it is pulled apart during anaphase.
Term
Diplo-X egg
Definition
An egg with two X chromosomes, a result of chromosome non-disjunction. In Drosophila, fertilization of such an egg leads to XXY females or XXX metafemales.
Term
Diploid (2n)
Definition

"Two fold"

Two alleles for each gene coexist in each cell. The adults of most eukaryotes are diploid. Most somatic cells contain two copies of the haploid genome.

Term
Dihybrid cross
Definition

"Two"

A cross that looks at two traits simultaneously. Shows that traits are not inherited together. Produces a phenotypic ratio of 9:3:3:1.

Term
Disulfide bonds
Definition
A covalent interaction that helps form tertiary structure in proteins.
Term
DNA
Definition

Deoxyribonucleic acid

A nucleic acid. The genetic material of virtually all organisms. First discovered by Friedrich Miescher. Structure was discovered by Watson and Crock. A right-handed double helix of polynucleotide strands, with hydrogen bonds holding the strands together. There is a major groove and a minor groove. Contains deoxyribose sugar, and the nitrogen-containing bases adenine, guanine, cytosine, and thymine. The two strands are anti-parallel and complementary. Has the ability to duplicate itself. It is housed in the nucleus and during cell division it is compacted into the chromosomes. One person has around 3 billion nucleotides in their DNA. DNA directs the function of RNA. Functional DNA is supercoiled.

Term
DNase
Definition
Deoxyribonuclease. An enzyme that breaks down DNA.
Term
Domains
Definition
Loops in the negative supercoiling of the folded genome of a bacterium. There are 50 - 100 in a bacterial genome.
Term
Dominant allele
Definition
An allele that has the same phenotypic effect on a heterozygote as on a homozygote. Phenotypes appear in every generation of a pedigree.
Term
Dominant epistasis
Definition
Epistasis where a dominant allele in the epistatic genes masks the genotype of the hypostatic gene. A_B_ and A_bb both produce the same phenotype. It doesn't matter what the B genotype is when the A gene is A_. Prouces a 12:3:1 ratio from a dihybrid cross.
Term
Dominant hypermorphic allele
Definition
A form of dominant mutation. Negative phenotype consequences due to the over-production of a normal protein, or a negative phenotype consequences due to the production of a protein with increased activity levels.
Term
Dominant lethal allele
Definition
A lethal allele where both heterozygotes and homozygotes die. Example: Huntington's disease.
Term
Dominant mutation
Definition
A mutation that is dominant. Includes dominant hypermorphic alleles, neomorphic alleles, and dominant-negative alleles.
Term
Dominant-negative alleles
Definition
A form of dominant mutation. A protein is produced which interferes with the wild-type protein (in heterozygotes) by inhibiting, antagonizing, or limiting their activity. Example: T gene in mice.
Term
Donkey
Definition

Equus asinus

2n = 62

Crossed with a horse to produce a mule.

Term
Donor cell
Definition
The bacterium which gives some DNA to the recipient cell in a recombination event with bacteria.
Term
Dosage compensation
Definition
How organisms equalize gene expression in sex chromosomes. Either the expression of the X chromosome is increased in one, decreased in both, or completely inactivated in both.
Term
Down syndrome
Definition

47, +21

Trisomy in chromosome 21. The only autosomal chromosome nondisjunction disorder with adult survivors, and the best known trisomy in humans. First descrbed in 1866 by Langdon Down, but wasn't understood until 1959. Occurs in 1/700 people. 96% of cases are due to meiotic nondisjunction events: 80% of these in oogenesis in the mother, and 20% in spermatogenesis in the father. The longer the prophase arrest in the mother (the older the mother), the higher the  likelihood of Down syndrome. Short stature, loose and hyperflexible joints (especially ankles), broad skulls, wide nostrils, large tongues with distinctive furrowing, epicanthal folds, stubby hands with a crease in the palm, impaired mental abilities requiring special education and care, a reduced lifespan, and early onset of Alzheimer's disease at age 40 - 50.

Term
Dr. Lee Reichman
Definition
Called multi-drug resistant tuberculosis a "time-bomb".
Term
Drosophila melanogaster
Definition

Fruit flies

A test organism that has been used to centuries. There are four pairs of chromosomes, one of which are sex chromosomes. Two pairs of the autosomes are large and metracentric; the other pair is small and dot-like.

Term
Drosophila virilise
Definition
A close relative of Drosophila melanogaster. One pair of sex chromosomes, and four pairs of acrocentric autosomes.
Term
Duplication
Definition
Hyperploidy withh an extra chromosome segment. May be attached to a chromosome, or be a free duplication. Large duplication can be studied cytologically. In Drosophila, duplications can be studied in polytenes.
Term
Duplication mapping
Definition
A form of cytogenetic mapping. A duplication covers a recessive mutation, localizing the gene within the boundaries of the duplication.
Term
Durum wheat
Definition
A variety of emmer wheat that is used in pastas, semolina, and couscous.
Term
Edmund Beecher
Definition
A cytologist. One of the first people to investigate the genetic differences between the sexes.
Term
Edward Adelburg and Sarah Burns
Definition
First identified F' factors in 1959.
Term
Edward syndrome
Definition

47, + 18

Trisomy in chromosome 18. Occurs in 1/8,000 people. Serious phenotypic abnormalities which cause death within a few weeks: congenital malformation of many organs including brain and heart, low-set and malformed ears, receding mandible, small mouth and nose with an elven appearance, mental deficiency, horseshoe or double kidney, short sternum, clenched hands, rocker bottom feet. 90% of individuals die within the first six months after birth.

Term
Egg
Definition
One is produced from a meiosis event in females.
Term
Elie Wollman and François Jacob
Definition
Worked at the Pasteur Institute in Paris in 1957. Crossed Hfr H cells with F- cells, and distrubed conjugation at various times to study the timing of conjugation.
Term
Elongation (transcription)
Definition
The second phase of transcription. Nucleotides attach to RNA polymerase, forming a complementary RNA strand based on the DNA sequence.
Term
Elongation (translation)
Definition
The second phase of translation. The ribosome moves down the mRNA one codon at a time. Petpide bonds form between the amino acids deposited by tRNA, forming an RNA strand.
Term
Emmer wheat
Definition

Triticum turgidum

4n = 28

Produced froma cross between wild einkorn and wild wheat. Cultivated for 10,000 years. High protein, low lysine, does poorly in poor soils. There are many varieties, including durum wheat. Crossed with Triticum tauschii to produce bread wheat. Crossde with rye to produce triticale.

Term
Endomitosis
Definition
Certain tissues become polyploid during develompent. Chromosomes double and separate, but no cytokinesis occurs.
Term
Enzyme
Definition
Proteins that catalyze biochemical reactions.
Term
Episome
Definition
Similar to a plasmid, but can replicate autonomously or as a part of the main chromosome. Non-essential to the host. Includes lysogenic prophages.
Term
Epistasis
Definition

"Stand above"

When one allele masks the genotype of another. The epistatic gene masks the hypostatic gene. Can be recessive or dominant. Example: cinnabar mutation in Drosophila is epistatic over the white gene.

Term
Epistatic gene
Definition
In epistasis, the gene which does the masking.
Term
Erwin Chargaff and colleagues
Definition
Analyzed the composition of DNA from many organisms and found that the concentration of thymine always equalled the concentration of adenine, and the concentration of cytosine always equalled the composition of guanine.
Term
Escherichia coli
Definition

E. coli

A bacteria. Infected by bacteriophages T4 and lambda. Can use almost any sugars as an energy source. Some mutants are unable to grow on certain sugars alone. Some mutants are resistant to antibiotics. Wild-types are prototrophs, and some mutants are auxotrophs.

Term
Euchromatin
Definition

"True"

Chromatin that dyes a light colour.

Term
Euploid
Definition
"Good fold"Having a complete set of chromosomes.
Term
Exon
Definition
Coding sequences of RNA. After introns are removed, exons are spliced together.
Term
Expressivity
Definition
The degree to which a phenotype is expressed (mild to serve). Describes individual variability.
Term
Extensively drug-resistant (XDR)
Definition
Bacterial diseases resistant to antibiotics used to treat for MDR strains.
Term
F+ cell
Definition
A bacterial cell which contains an autonomous F factor.
Term
F- cell
Definition
A bacterial cell which does not contain an F factor. It may become F+ or Hfr if it is the recipient cell in conjugation with either type.
Term
F factor
Definition

Fertility factor

A plasmid that codes for an F pili on the donor cell in cojugation. About 105 nucleotides in size. May be in an autonomous state or integrated state.

Term
F' factor
Definition
An F factor which was excised from an Hft erroneously, bringing with it some bacterial genes. Ranges in size from a singel gene to up to half the bacterial chromosome. First identified by Edward Adelberg and Sarah Burns.
Term
F pili
Definition
A structure in the donor cell which establishes contact with the recipient cell in conjugation. Coded for by the F factor.
Term
F.W. Robertson
Definition
Discovered Robertsonian translocation.
Term
F1 generation
Definition
The offspring of the P generation. In the formation of hybrids, only the dominant trait is visible in 100% of the offspring.
Term
F2 generation
Definition
The offspring of a self-fertilization of individuals from F1. Progeny show a ratio of 3:1, the Mendelian ratio.
Term
Fertilizing organs
Definition
Parts of teh sugar snap pea flower. Contains the eggs. They are tighly packed into the keel petal, preventing foreign pollen from fertilizing the eggs.
Term
Fibrous protein
Definition
Proteins that are shaped like long strands.
Term
Flower colour
Definition
One of the seven traits Mendel looked at in the sugar snap peas. Flowers are either purple or white.
Term
Flower position
Definition
One of the seven traits Mendel looked at in sugar stnap peas. Flowers (and pods) are either axial (along the stem) or terminal (at the top of the stem).
Term
The genome
Definition
The functional state of the bacterial genome. The circular DNA is highly supercoiled, and folded into 50 - 100 domains held together by single-stranded nicks, RNA, and proteins.
Term
Frederick Griffith
Definition
Discovered transformation in 1928 in Streptococcus pneumoniae when he discovered that non-virulent bacteria could take up a "transforming principle" from dead virulent bacteria, and make them virulent.
Term
Frederick Sanger
Definition
Discovered insulin in 1953.
Term
Free duplication
Definition
Duplication where the extra chromosome segment is a new, separate chromosome.
Term
Friedrich Miescher
Definition
Discovered DNA in 1869. Called it "nuclein".
Term
G1 phase
Definition
The first phase of interphase. Cell increases in size, organelles are duplicated, molecular machinery for DNA replication is assembled.
Term
G2 phase
Definition
The third phase of interphase. Continued cell growth. Centrosome duplication is completed and chromosome condensation begins.
Term
Gain-of-function mutation
Definition
A dominant mutation that creates a new polypeptide with a new function. Example: Antennapedia
Term
Galactose
Definition
Present on the surface of red blood cells of individuals with an IB allele: type B and AB blood.
Term
George Beadle and Edward Tatum
Definition
Discovered that the product of genes are polypeptides.
Term
George Shull
Definition
A plant breeder who began the practice of crossing inbred lines in crops to produce hybrids with heterosis. This is now a standard procedure in the crop breeding industry.
Term
Gene
Definition
The fundamental unit of heredity. Sections of DNA that specify instruction for synthesis of polypeptides or RNA molecules. Comes in multiple alleles. Helps determine a characteristic. Passed from parent to offspring.
Term
Gene expression
Definition
The phenotypic function of genetic material. Controls the development of phenotypes. Must dictate growth of the organism.
Term
Generalized transduction
Definition
Transduction where a random fragment of bacterial DNA is packaged into the phage in the place of the phage chromosome. The transducing particle contains only bacterial DNA. Any gene may be transferred. Frequency of generalized transduction for any given gene is 1 in 106 bacteriophage particles.
Term
Genetic interaction
Definition
Different combinations of alleles from two or more genes resulting in different phenotypes due to interactions between their products.
Term
Genetic map
Definition
A type of chromosome map. A linkage map based on calculations of frequencies of genetic recombination.
Term
Genetic map unit
Definition
The distance between two points on a genetic map. The average number of crossovers that occur between them. Units are centiMorgans.
Term
Genetic material
Definition
Must replicate, express genes, and mutate. In most organisms it is DNA.
Term
Genetic mosaic
Definition
In female mammals, about half the body has the maternal X chromosome inactivated, and half the body has the paternal X chromosome inactivated. This may lead to mosaicism.
Term
Genetics
Definition
Plays a critical role in understanding diseases. Improves agricultural practices. Used for biotechnology industry for drug design, development, and production.
Term
Genomic map
Definition
A type of chromosome mapping. Contains the entire nucleotide sequence of a genome.
Term
Genotype
Definition
The set of alleles possessed by an individual organism. Confers phenotype.
Term
Giesma
Definition
G-banding. A stain used in cytogenetics. A mixture of dyes named after their inventor, Gustav Giemsa. Produces unique bands on chromosomes.
Term
Globular protein
Definition
A protein which is more or less spherical.
Term
Gregory Johann Mendel
Definition
A monk who lived in the mid-1800s. The "Father of Genetics". He did experiments with sugar snap peas plants in his abbey garden, which lead to the deduction of fundamental laws of genetics.
Term
Guanine (G)
Definition
A nitrogen-containing base found in DNA and RNA. A purine: has two rings, with one =O. Pairs with cytosine with three hydrogen bonds. Its nucleotide is dGMP.
Term
Gustav Giemsa
Definition
Invented Giemsa, a dye used in cytogenetics.
Term
Gynandromorphs
Definition

"Woman-man forms"

Drosophila flies with male and female structure.

Term
Habsburg jaw
Definition

aka Prognatism

Normal varitations in the size of the mandible can be pathological if extreme. Frequent in the Habsburg royal family, peaking at Phillip II and Charles I of Spain; the family was inbred. It is clearly a heritable trait, but details are unknown. Authors studied 2,562 individuals from 55 families. Most pedigrees suggest autosomal dominant inheritance with incomplete penetrance. There is a major gene that influences expression of prognatism with clear signs of Mendelian inheritance and a multifactorial component. Has low heritability.

Term
Haemophilia
Definition
A disease caused by inablity to produce a factor needed for blood clotting. Cuts, bruises, and wounds continue to bleed, and can lead to death if the individual is not transfused with a clotting factor. In the past, haemophiliacs would die before age 20, now they can live long, healthy lives. It is caused by a recessive X-linked mutation. Nearly all affected individuals are male. It is found in the Russian IMperial family, transmitted from Queen Victoria of Great Britain.
Term
Haemophilus influenza
Definition
A bacteria which displays transformation. Will take up only specific, short DNA sequences from their own species or closely related species.
Term
Hand pollination
Definition
Mendel performed cross-fertilizations on sugar snap peas by hand, but removing the keel petal and anthers with forceps and dusting pollen onto the stigma.
Term
Haplo-diplo system
Definition
The sex determination system in honeybees and wasps. Sex is determined based on whether the animal is haploid or diploid. Females are diploid, and males are diploid. Whether a female becomes a reproductive queen or a sterile worker depends on how she was nourished as a larva. Males are produced from unfertilized eggs; the queen can control how many males are produced by controlling how many eggs are fertilized.
Term
Haploid (n)
Definition
One allele for each gene exists in each cell in a eukaryote. The gametes of most eukaryotes are diploid. The basic chromosome number. Varies among species. The number of chromosomes is unrelated to the size and complexity of the organism. Most species have between 10 and 40 chromosomes.
Term
Haploid genome
Definition
One set of chromosomes.
Term
Haploinsufficiency
Definition
When the null allele is dominant over the wild-type allele. Just one wild-type allele cannot produce enough protein to show the wild-type phenotype.
Term
Haplosufficiency
Definition
When the wild-type allele is dominant over the null allele. Just one wild-type allele can produce enough protein to show the wild-type phenotype.
Term
Hard red spring wheat
Definition
A variety of bread wheat that is used to make bread flour.
Term
Hard red winter wheat
Definition
A variety of bread wheat that is used to make all-purpose flour.
Term
Hard white wheat
Definition
A variety of bread wheat used to make bread, and is used in brewing.
Term
Hardy Weinberg equilibrium
Definition

Predicts genotypes through alleles frequencies of a population. Allele frequencies stay constant if there are no evolutionary influences: non-random mating, unequal survival, population subdivision, and migration.

f(A) = p

f(a) = q

p2 + 2pq + q2 = 1

Term
Heinz Fraenkel-Conrat and coworkers
Definition
Discoverd that RNA was the genetic material of some viruses in 1957, using experiments on tobacco mosaic virus. The protein coat of the virus could be replaced and the prgeny phages were of the same strain type as the RNA.
Term
Harriet Creighton and Barbara McClintock
Definition
In 1931, found evidence that recombination is a material exchange between chromosomes. Studied homologous chromosomes in maize that were morphological distinguishable. Chromosome 9 has two forms: normal and one with a knob and different-looking chromosome. These markers were linked with the genes for kernel colour and kernel texture. Recombined progeny have swapped markers.
Term
Helical
Definition
A secondary structure in proteins. Alpha helix shape, maintained by hydrogen bonds.
Term
Hemoglobin
Definition
A transport protein that trasnports oxygen. Consists of two identical alpha chains and two identical beta chains held together to form a quaternary structure. A globular protein.
Term
Hemizygote
Definition
An organism with one copy of gene, such as a male individual with one X chromosome.
Term
Henry H. Turner
Definition
An organism with one copy of a gene, such as amel individual with one X chromosome.
Term
Heterochromatin
Definition

"Different"

Chromatin that dyes a dark colour.

Term
Heteroduplex
Definition
A DNA strand where the strands have different sequences. Can form in tranfsormation if the donor cell has a different allele than the recipient cell on the locus. The two different strands will segregate into different daughter cells when the cell divides.
Term
Heterogametic sex
Definition
The sex which produces two types of gametes. In humans and Drosophila it is males. In birds, butterflies, and some reptiles it is females.
Term
Heterogeneous trait
Definition
A recessive mutation in any one of two or more genes, giving rise to the same phenotype. It is detected by a complementation test. The F2 generation of a complementation cross have a phenotypic ratio of 9:7. Example: deafness; there are about 50 genes in humans that can lead to deafness.
Term
Heterosis
Definition
A term coined by George Shull. Vigour found in hybrids produced by crossing two inbred lines. The individuals are heterozygous for many traits, giving hybrid vigour.
Term
Heterozygous
Definition
Possessing two different alleles at a locus. All individuals in F1 are heterozygous. 50% of F2 individuals are homozygous.
Term
Hexaploid (6n)
Definition

"Six fold"

Having six sets of chromosomes. Oats and bread wheat are hexaploid.

Term
Hfr cell
Definition
High frequency recombination cell. A bacterial cell which has an F factor in integrated state, in the bacterial chromosome. The F factor may be excised in a reverse process from integration, sometimes forming an F' factor.
Term
Himalayan
Definition

chch

A rabbit coat colour. A temperature sensitive mutation. In rabbits reared at 20ºC or lower, dark pigment is produced at theextremities of the rabbit: ears, face, and legs. In rabbits reared at higher temperatures, the coat is white all over. The enzynme that produces the dark pigments is inactivated and higher temperatures.

Term
Histones
Definition
A component of chromatin. Basic, positively charged proteins. Present in all eukaryotes in amounts equal to the amount of DNA, with a few exceptions: in sperm cells they are replaced by protamines. Have five classes: H1, H2a, H2b, H3, and H4, present in a 1:2:2:2:2 ratio. Forms nucleosome complexes with DNA. There are only 4 - 5 different types of nucleosomes in the whole kingdom of Eukarya. Small changes in the structure of histones alters gene expression.
Term
Homogametic sex
Definition
The sex which produces one type of gamete. In humans and Drosophila it is females. In birds, butterflies, and some reptiles, it is males.
Term
Homologous chromosomes
Definition

aka Homologs

Chromosome containing the same genetic code for the same traits, together in a pair in a diploid cell.

Term
Homozygous
Definition
Having two of the same allele at a locu.
Term
Homozygous dominant
Definition

AA

Having two dominant alleles. ONe of the P generation parents is homozygous dominant. 25% of F2 indivuduals are homozygous dominant.

Term
Homozygous recessive
Definition

aa

Having two recessive alleles. One of the P generation parents is homozygous recessive. 25% of F2 individuals are homozygous recessive.

Term
Hore
Definition

Equus caballus

2n = 64

Crossed with a donkey to produce a mule.

Term
Human Genome Project
Definition
A product to map all the genes of humans. Took over 10 years and $3 billion. Unlocks vast analytic power. We now have genomes that we can reference. There are medical and security applications.
Term
Huntington's disease
Definition
A rare autosomal dominant lethal allele. A hypermorphic allele. A neuro-degenerative disease. Increased amounts of a protein are produced, and they clump up in the brain, caused loss of muscle co-ordination, cognitive decline, and dementia. Shows variable expressivity in time of onset.
Term
Hybrid
Definition
Offspring from two crossed inbred lines, of from a true-breedng P generation.
Term
Hydrogen atom
Definition
A component of an amino acid. It is attached to the central carbon.
Term
Hydrogen bonds
Definition
A non-covalent interaction that helps from tertiary structure in proteins.
Term
Hyperactivation
Definition
The dosage compensation method found in Drosophila. The genes on the X-chromosome have increased activities in males.
Term
Hypermorphic allele
Definition
Gain-of-function allele. Produces a protein that has increased function. This can be bad for the orgnaism. Example: Huntington's disease.
Term
Hyperploid
Definition

"Over-fold"

Aneuploidy where a chromosome or chromosome segment is over-represented.

Term
Hypomorphic allele
Definition

"Beneath form"

A partially functional allele. A poorly functioning protein a produced, or reduced amounts of a normally functioning protein is produced. A mild mutant phenotype.

Term
Hypoploid
Definition

"Under-fold"

Aneuploidy where a chromosome or chromosome segment is under-represented.

Term
Hypostatic gene
Definition
In epistasis, the gene that is masked.
Term
Identity by descent
Definition
When an inbred individual inherits both alleles of a gene from one common ancestor. These genes are homozygous.
Term
Ideogram
Definition
The pattern of banding on a chromosome when dyed with quinacrine or Giemsa.
Term
Inactivation
Definition
The dosage compensation method found in placental mammals (including humans). One of the X chromosomes in the female is inactivated. First proposed by Mary Lyon. When the female individual is a few thousand cells in size, each cell makes an independent decision of which X chromosome to inactivate, and after this point all the daughter cells have the same X chromosome inactivated. Female mammals are genetic mosaics. The X chromosome is inactivated by bethyl groups and condenses into a Barr body. In XXX females, two X chromosomes are inactivated.
Term
Inbred
Definition
Offspring from consanguineous matings. Have one or more common ancestors. Genes may have identity by descent.
Term
Inbred lines
Definition
Created by mating siblings, generation after generation, such  as in guinea pigs or rats. Individuals are genetically pure, but often have inbreeding depression. Crossing inbred lines can produce heterosis.
Term
Inbreeding
Definition
Can be used to look at homozygous effects of alleles, but it effects the character of plant and animal populations. Increases the frequency of homozygotes. In some human cultures it is encouraged to preserve the purity of bloodlines, such as royalty. Example: ancient Egypt, Polynesia, the Amish.
Term
Inbreeding coefficient (F)
Definition

Invented by Sewall Wright in 1921. Involves the analysis of correlations between individuals in a pedigree. In the 1940s Charls Cotterman showed that it is the same as the probability of identity by descent. An increased F value results in increase in probability of recessive disorders. It can be used to measure the decline in complex phenotypes, by graphing phenotypes with F as the x-axis; traits decline linearly. To find F of an inbred individual.

1. Identify common ancestor(s) of inbred individual, connected to both parents.

2. Count the number of individuals in each inbreeding loop (one loop for each common ancestor). Do not count the inbred individual.

3. Calculate ½n, and add up these values for each inbreeding loop

4. If the common acnestor is inbred, multipy ½n b (1+FCA), where FCA is the F value of the common ancestor. This accounts for the possibility that the genes are already identical by descent.

Term
Inbreeding depression
Definition
A loss in vigour often found in inbred lines. Found in plants which are self-pollinated over many generations, or test animals that have been inbred for several generations. Example: inbred corn plants are shorter and produce small ears with fewer kernels.
Term
Inbreeding loops
Definition
Loops formed in pedigrees where there is inbreeding.
Term
Incomplete dominance
Definition

aka Partial dominance

When a heterozygote has a different phenotype from either the dominant or recessive homozygote. Includes semidominant. Produces a 1:2:1 ratio from a monohybrid cross.

Term
Incomplete penetrance
Definition
Not all individuals with identical known genotypes produce the expected phenotype. Can lead to problems in pedigree analysis. Example: polydactyly.
Term
Initiation (transcription)
Definition
The first stage of transcription. RNA polymerase binds to the promoter region of DNA, and unwinds the DNA.
Term
Initiation (translation)
Definition
The first stage of translation. The mRNA enters the cytoplas through nuclear pores, and binds to a small ribosomal subunit. A tRNA carrying the amino acid methionine (codon AUG) binds to the complex. A large ribosomal subunit attaches to the complex.
Term
Insulin
Definition
A regulatory protein consisting of an alpha chain, beta chain, and an intervening C-peptide. Regulates the uptake of glucose into cells. A single peptide is attached on the end during synthesis in the endoplasmic reticulum and Golgi apparatus. Insulin was discovered by Frederick Sanger.
Term
Integrated state
Definition
An F factor which is inserted into the bacterial chromosome. Cells with integrated F factors aare Hfr cells. In conjugation the entire chromosome may be transferred to the recipient cell, but is often broken in the process. The F factor is integrated first.
Term
Interference (I)
Definition
Cross-over inhibited by the occurrence of anohter, nearby cross-over. Measured by the coefficient of coincidence. Strong between markers less than 20 cM distance. Strength of interference is a function of map distance.
Term
Interkinesis
Definition
The fifth stage of meiosis I. A short interphase period between meiosis I and II.
Term
Interphase
Definition
One of hte phases of cell cycle. DNA is duplicated and other biochemical processes occur, preparing the cell for division. Includes G1 phase, S phase, and G2 phase.
Term
Intersex
Definition
Drosophila flies with a rato of X chromosomes to autosomes between 0.5 and 1.0 show characteristics of bot sexes.
Term
Intron
Definition
Non-coding sequences of RNA. They are removed after transcription.
Term
Inversion
Definition
Chromosome rearrangement where the orientation of a segment within a chromosome is switched; a transposabl element becomes detached and reattaches the opposite direction. The order of genes is reversed. May be induced with X-ray radiation, or may occur naturally from mechanical shear as a result of chromosome entanglement in the nucleus. Includes pericentric and paracentric inversions.
Term
Inversion heterozygote
Definition
A cell where one of the chromosomes has an inversion and the other does not. During meiosis, one of the chromosomes forms a loop to allow for pairing of the inverted regions.
Term
Ionic bond
Definition
A non-covalent interaction that helps form tertiary structure in proteins.
Term
Isochromosome
Definition
A compound chromosome formed from the union of two homologous chromosome segments that meet in the centromere. The two arms are the same.
Term
James Watson and Francis Crick
Definition
First described the double-helix structure of DNA in 1953. Won the Nobel Prize in 1962, along with Maurice Wilkins. Used two pieces of evidence: one from Erqin Chargaff and colleagues, and one from Maurice Wilkins, Rosalind Franklin, and coworkers.
Term
J.H. Renwick and S.D. Lawler
Definition
In 1955, analyzed the evidence of linkage between ABO blood groups and Nail-Patella syndrome. The allele for type B blood is linked to NPS1, the gene for Nail-Patella syndrome. The genetic map distance between the genes can be crudely calculated using pedigrees.
Term
Johann Friedreich Miescher
Definition
A Swiss medical student who in 1868 studied abscidic substances: treated pus cells from used bandages with pepsin isolated from pig stomachs. Recovered an abscidic substance that he called "nuclein", which contained large amounts of nitrogen and phosphorus: DNA.
Term
Joshua Lederberg and Edward Tatum
Definition
Discoverd conjugation in E. coli.
Term
Joshua Lederberg and Norton Zinder
Definition
In 1952, discovered transduction in Salmonella typhimurium. Bacteria could pass genes for amino acid synthesis even when separated by a U-tube, only when one of the strains was infected with bacteriophage P22.
Term
Karyotype
Definition
A pictorial display of the chromosomes, photographed at metaphase, arranged from largest to smallest. Made with Giemsa or chromosome painting. There are 23 chromosomes in the human karyotype.
Term
Keel petal
Definition
A part of the sugar snap pea flower. A modified petal which is tightly packed around the fertilizing organs, preventing foreign pollen from fertilizing the eggs.
Term
Keratin
Definition
A structural protein made of two helical strands. Found in hair, horns, feathers, and hooves.
Term
Kinetochore
Definition
Constrictions at the centre of sister chromatids. Where microtubule spindles attach.
Term
Klinefelter syndrome
Definition
Caused by an XXY genotype. There are 47 chromosomes. First described by H.F. Klinefelter in 1942. Individuals are male. Occurs in 1/500 male births. Usually sterile, with some feminized secondary sexual characteristics: small testes, enlarged breasts, long limbs, knock-knees, underdeveloped body hair, feminine-pitched voice. There are one or more Barr bodies in the cells. Treated with testosterone therapy and breast tissue removal. Caused by fertilization of a diplo-X egg with a Y sperm, or a normal egg with an XY sperm. Genotypes that can also caused Klinefleter syndrome: XXYY, XXXY, XXXYY, XXXXY, ,XXXXYY, and XXXXXY.
Term
Langdon Down
Definition
First described Down syndrom ein 1866.
Term
Latyrus odorantus
Definition
A flower that shows epistasis for colour. If either the C or P gene is homozygous recessive, flowers are white, but if both genes have at least one dominant allele, the flowers are purple, resulting in a 9:7 ratio from a dihybrid cross. Both genes produce proteins that are necessary for production of anthocyanin. If either gene is missing, anthocyanin cannot be produced. The fact that there are two genes involved was determined by a complementation test.
Term
Lethal mutation
Definition
A mutation on an essential gene. Leads to death. Lethal mutations that act early in life are lost after one generation, but lethal mutations that act later in life, after reproduction, may be passed on. May be recessive or dominant.
Term
Lft lysate
Definition
Low frequency transduction. A bacteriophage which has had specialized transduction, but it retained its lytic genes, allowing it to become lytic in the host. Occurs once every 106 progeny phages.
Term
Lillian Morgan
Definition
The wife of T.H. Morgan. Discovered compound chromosomes in 1922. Studied attached-X chromosomes in Drosophila.
Term
Linkage
Definition
When two genes are on the same chromosome.
Term
Linkage phase
Definition
The way in which alleles are arranged in heterozygous individuals. Coupling or repulsion.
Term
Linkers
Definition
DNA between nucleosomes. 8 - 114 nucleosome pairs. Susceptible to DNase.
Term
Lipid
Definition
A biological macromolecule.
Term
Lobe
Definition
A mutation in the eye shape of Drosophila. It can show variable expressivity. Some heterozygotes have normal eyes, some have smaller and misshapen eyes, and some have no eyes at all.
Term
Locus
Definition
A specific location on a chromosome, occupied by an allele.
Term
Lysogenic phage
Definition
Viral DNA is inserted into the chromosome of the host bacterium with a site-specific recombination event, becoming a prophage. Once every 105 divisions, the prophage becomes lytic: a recombination event occurs that removes the prophage. Sometimes bacterial DNA can erroneously come with it, transducing bacterial genes to other bacteria.
Term
Lysozyme
Definition
An enzyme produced by viral DNA of a lytic phage, which degrades the cell wall of the host bacterium, releasing progeny phages.
Term
Lytic phage
Definition
Replicates viruses and kills the host. Proteins for transcription, translation, and replication of bacterial genes shuts down about 2 minutes after injection, then production of progeny phages begins and they accumulate in the cell about 17 minutes after injection. At about 25 minutes, lysozyme breaks the bacterial cell wall, releasing 300 progeny per infected cell. Chromosomes can be mapped by infecting a bacterium with two strains of the virus simultaneously and observinv recombination frequencies.
Term
Mad Cow Disease
Definition

Bovine spongiform encephalopathy (PSE)

A disease that destroys brain tissues and leads to death in cattle. In sheep and goats it is called scrapie. Caused by prions. Can be passed to humans by eating meat from infected cattle. In humans it is called Creutzfeldt-Jakob disease. All animals have the normal prion, PrPC. The disease form of the prion is PrPSc, and it converts helathy prions into diseased prions and accumulates int he brain, causing nerve cells to die, leading to a "spongy" appearance of the brain tissue.

Term
Manx
Definition

A recessive lethal allele in cats that also affects tail development.

mm: normal cat

Mm: Manx cat

MM: lethal

Term
Marker
Definition
A physical attribute on a chromosome which is linked to a gene, allowing it to be studied cytologically.
Term
Mary Lyon
Definition
First proposed that dosage compensation is achieved by inactivation of one X chromosme in females. Inferred this from research on mice; studied genetic mosaic female mammals.
Term
Maurice Wilkins, Rosalind Franklin, and coworkers
Definition
Franklin died in 1953, so could not be awarded the Nobel Prize in 1962 with Watson, Crick, and Wilkins. Took the X-ray diffraction pattern of DNA, indicating that DNA was highly ordered, two-stranded, with repeating substructures of 0.34 nm.
Term
Meiosis
Definition
Occurs only with sexual reproduction that takes place in the reproductive organs of plants and animals. For humans, the ovaries and testes. Each parent contributes half of their genes. For humans, 23 of the 46 chromosomes. The offspring created is genetically different from each parent. Results in four haploid daughter cells. In males it produces sperm and in females it produces polar bodies and eggs. Has two phases: meiosis I and meiosis II.
Term
Meiosis I
Definition
The first phase of meiosis. Homologous pairing. Crossing over occurs. Introduces genetic variation. Reduces chromosome numbre from dipoid to haploid. Has five phases: prophase I, metaphase I, anaphase I, telophase I, and interkinesis.
Term
Meiosis II
Definition
The second phase of meiosis. Separation of sister chromatids, distribution into four daughter cells. Has four phases: prophase II, metaphase II, anaphase II, and telophase II.
Term
Meiotic interphase
Definition
The phase between meiosis. Chromosomes have been replicated in S phase.
Term
Mendel's Principle of Dominance
Definition
Individuals from F1 will show only phenotype of the dominant allele.
Term
Mendel's Principle of Independent Assortment
Definition

Mendel's Second Law

Different genes are inherited separately from one another. Mendel showed this with dihybrid crosses. There are many possible ways for chromosomes to be separated during anaphase of meiosis in heterozygous individuals, each equally likely.

Term
Mendel's Principle of Segregation
Definition

 Mendel's First Law

Alleles are passed on to offspring unchanged, and segregate into gametes independently. During meiotic division, homologous chromosomes pair, and in anaphase they separate and move to opposite poles.

Term
Mendel's Principles of Heredity
Definition
An English translation and summary of Mendel's findings, published by William Bateson in 1909. Examines the results of breeding experiments with many different plants and animals, demonstrating that Mendel's principles apply to all of them.
Term
Mendelian ratio
Definition
A ratio of 3:1 seen in the F2 generation.
Term
Messenger RNA (mRNA)
Definition
A type of RNA. It is the intermediary between DNA and polypeptides. After it is transcribed it goes into the cytoplasm and attaches to ribosomes which translate it into polypeptides. Has codons which code for amino acids.
Term
Metaphase
Definition
The third phase of mitosis. Kinetochore microtubules move the chromosomes to the spindle equator where they become aligned in the metaphase plate. This is the phase where a karyotype may be taken.
Term
Metaphase I
Definition
The second phase of meiosis I. Homologous chromosomes are pulled away by microtubules, and positioned on the cell's equator. Maternal and paternal partners align to poles randomly, further adding genetic variation.
Term
Metaphase II
Definition
The second phase of meiossis II. Exactly the same as mitotic metaphase.
Term
Metaphase chromosome
Definition
During metaphase, the chromosome is condensed.
Term
Metaphase plate
Definition
The arrangement of chromosomes midway between the two poles during metaphase.
Term
Metracentric chromosome
Definition
A chromosome with the centromere near the middle of the chromatids.
Term
Migration
Definition
An evolutionary influence that can cause Hardy Weinberg principle to be false.
Term
Mitosis
Definition

M phase

One of the phases of cell cycle. Includes prophase, prometaphase, metaphase, anaphase, and telophase. Produces clone daughter cells. All organisms use mitosis to grow and repair themselves.

Term
Molecular biology
Definition
Founded the study of bacteria and viruses.
Term
Monohybrid cross
Definition

"One"

A cross that looks at one gene.

Term
Monoploid
Definition
Having one set of chromosomes in a prokaryote. Bacteria are monoploid.
Term
Monsomy
Definition
Hypoploidy where one chromosome is missing. Includes Turner syndrome. In humans, all autosomal monosomies result in early miscarriage.
Term
Mosaicism
Definition
A phenotype of female mammals heterozygous on an X-linked gene. The female is a genetic mosaic. Example: tortioseshell cats.
Term
Movement
Definition
One of the functions of proteins. Contraction. Includes actin and myosin in muscle tissue.
Term
Mule
Definition

2n = 63

Sterile. Created from a cross between a donkey and a horse. Hardy and strong. Farm mechanization caused a rapid decline in mule production.

Term
Multi-drug resistant (MDR)
Definition
Bacterial diseases resistant to most normally prescribed antibiotics. Dr. Lee Reichman called it a "time-bomb".
Term
Multineme model
Definition

aka Multistrand model

Many strands of DNA run parallel through the chromosome. There is no evidence to support this model.

Term
Multiple alleles
Definition
When genes have more than two alleles. Example: coat colour in rabbits, human blood types. Alleles are symbolized by superscripts over the lowercase letter.
Term
Murray Barr and Ewart Bertram
Definition
The Canadian geneticists who discovered the Barr body in 1949.
Term
Mutant
Definition
Any allel which is not the wild type. Genes are often named for mutant alleles. Most mutant alleles are recessive.
Term
Mutation
Definition
The evolutionary function of genetic material. Changes to the genetic state. May affect phenotype, or not. Changes in phenotype are not always a result of mutation. Mutations can have a wide range of effects. They provide the raw material for evolution, allowing organisms to adapt and modify to their environment. Mutated genes produce polypeptides that are absent or altered in some way. Whether it is dominant or recessive depends on the nature of the mutation. Includes visible, sterile, letahal, loss-of-function, temperature sensitive, dominant-negatiev, and gain-of-function mutations.
Term
Nail-Patella syndrome
Definition
Caused by a rare dominant allele NPS1 on chromosome 9, linked to ABO blood type. It is 20 map units away from the ABO blood type locus. Linked to B blood groups.
Term
Negative supercoiling
Definition
The DNA is wound left-handedly (opposite as the DNA). Almost all organisms have negative suprecoiling.
Term
Neisseria gonorrhoea
Definition
A bacteria which displays transformation. Will take up only specific, short DNA sequences from their own species or closely related species.
Term
Neomorphic alleles
Definition
A form of dominant mutation. Codes for an altered protein that has a new function in the organism.
Term
Nitrogen-containing base
Definition
A constituent of a nucleotide. Attaches to the pentose sugars. Pyrimidines or purines. Includes adenine, guanine, cytosine, thymine, and uracil.
Term
Non-histone chromosomal proteins
Definition
A component of chromatin. Heterogeneous, mostly acidic proteins. Composition varies by cell type. Doesn't play a central role in packaging DNA into chromosomes. Regulates expression of specific genes.
Term
Non-random mating
Definition
An evolutionary influence that can cause the Hardy Weinberg principle to be false.
Term
Nondisjunction
Definition
First studied in Drosophila by Calvin Bridges. Proves the Chromosome Theory of Heredity. Can occur on any chromosome. A mistake in meiosis that results in aneuploid gametes. The failure of chromosomes to disjoin during meiotic division. When it occurs in meiosis I, it causes two empty cells and two cells with two chromatids each. When it occurs in meiosis II, it causes two normal cells, one epty cell, and one with two chromatids. In human females, the longer prophase arrest (older the age of the woman), the higher the chances of a nondisjunction event. May result in diplo-X eggs, and nullo-X eggs.
Term
Norm of reaction
Definition
The range of phenotypes expressed by a single genotype under different environmental conditions. A phenotype can have both incomplete penetrance and variable expressivity. It can be caused by: interactions with other genes, environmental factors, age, sex, temperature, or chemicals.
Term
Nucleic acid
Definition
A biological macromolecule found in virtually all cells. It was proved to be the genetic material, rather than proteins, in the 1940s - 1950s. Information polymers are characterized by their interactions among themselves. Includes DNA and RNA. Made of nucleotides.
Term
Nucleosome
Definition
A complex of histones and DNA. A "bead" approximately 11 nm in diameter and 6.5 nm long. DNA wraps around a histone octomer 1¾ times in a negative supercoil, forming the nucleosome core. H1 histone holds the nucleosome core together, plus some more DNA, for a total of 200 nucleotide pairs associated with each nucleosome. Protects the DNA from nucleases.
Term
Nucleosome core
Definition
Exactly 143 nucleotide base pairs wrapped around a histone octomer in a nucleosome.
Term
Nucleotide
Definition
The building blocks of nucleic acids. Each is composed of a phosphate group, a pentose sugar, and a nitrogen containing base.
Term
Nucleus
Definition
The membrane-enclosed organelle where DNA is housed.
Term
Null allele
Definition

Amorphic allele

"Without form"

A non-functional allele. Almost always recessive. The protein product is not produced, or a non-functional protein is produced. Example: cinnabar mutation in drosophila. Null alleles can be dominant when there is haploinsufficiency.

Term
Nullo-X egg
Definition
An egg with no X chromosomes. A result of nondisjunction. In Drosophila, if fertilized it leads to XO males and YO males (die immediately).
Term
Octaploid (8n)
Definition

"Eight fold"

Having eight copies of the haploid genome. Commercial varieties of strawberries, and sugarcanes are ocatploid.

Term
Offspring of double first cousins
Definition

Inbred individuals

F = 1/8

Term
Offspring of first cousins
Definition

Inbred individuals

F = 1/16

Term
Offspring of full siblings
Definition

Inbred individuals with two common ancestors: the grandparents. There is one inbreeding loop in the pedigree.

F = 1/4

Term
Offspring of half siblings
Definition

Inbred individuals with one common ancestor: the common grandparent. There is one inbreeding loop in the pedigree.

F = 1/8

Term
Offspring of uncle and neice/aunt and nephew
Definition

Inbred individuals

F = 1/8

Term
Old World cotton
Definition

2n = 26

Originated in Asia and Africa. Crossed with American cotton to produce upland cotton.

Term
oriS
Definition
Performs the function of oriV if it is absent or non-functional.
Term
oriT
Definition

Origin of Transfer

The site in an F factor where DNA replication for transfer in conjugation is initiated.

Term
oriV
Definition
The site in a bacterial chromosome where DNA replication for fission is initiated.
Term
Oswald Avery, Collin MacLeod, and Maclyn McCarty
Definition
In 1944, showed that DNA was the genetic material. DNase was the only enzyme that could prevent transformation in bacteria.
Term
P arm
Definition
The long arm of a chromosome.
Term
P generation
Definition
The true-breeding parental generation.
Term
Paracentric inversions
Definition
Inversions that do not include the centromere. The relative lengths of the chromosome arms are not changed. Harder to detect cytologically than pericentric inversions.
Term
Parasexual processes
Definition
Unidirectional recombination events in bacteria. Includes transformation, conjugation, and transduction.
Term
Pataue syndrome
Definition

47, + 13

Trisomy in chromosome 13. Occurs in 1/20,000 births. Serious phenotypic abnormalities that cause death in a few weeks: mental deficiency, deafness, minor muscle seizures, cleft lip and/or palate, cardiac abnormalities, posterior heel prominence, large triangular nose, malformation of the brain and heart, polydactyly.

Term
Pattern baldness
Definition
A trait which is recessive in women (and often produces only hair thinning), but dominant in men. This is due to the gene's interactions with testosterone.
Term
Pedigree
Definition
A family tree. Used when analyzing human genetics. Can be used to generate genetic maps to track the inheritance of certain genes, genetic disorders, and other traits. Limited success for complex genetic traits.
Term
Penetrance
Definition
The proportion of individuals that have a particular genotype that express the expected phenotype. Describes the statistical variability among a population. Includes complete penetrance and incomplete penetrance.
Term
Penicillin
Definition
Discovered by Alexander Fleming. Caused a revolution in treatment of bacterial disease. Occurrence of tuberculosis decreased in the US in the 1970's.
Term
Pentaploid
Definition

"Five fold"

Having five sets of chromosomes. Some seedless varieties of citrus are pentaploid.

Term
Pentose sugar
Definition
One of the constituents of a nucleotide. Attaches the phosphate group to the neighboring nucleotide. The nitrogen containing-base is attached to the pentose sugar. Deoxyribose or ribose.
Term
Peptide bonds
Definition
The bonds which bind amino acids together in a polypeptide. Forms between the amino group of one amino acid and the carbocyl group of another. A molecule of water is formed when peptide bonds form.
Term
Pericentric inversion
Definition
An inversion that includes the centromere. May change the relative lengths of the two arms of the chromosome. Acrocentric chromosomes may be turned into metracentric chromosomes and vice versa. Easier to detect cytologically than paracentric inversions.
Term
Phenocopy
Definition
When environmental factors alone cause a phenotype that mimics the effect of a genetic mutation. Example: thalidomide.
Term
Phenotype
Definition

Trait

The appearance or manifestation of a characteristic. Conferred by genotype. It has some measure of penetrance and some measure of expressivity. One genotype can have a wide norm of reaction.

Term
Phenylalanine
Definition
An amino acid which cannot be metabolized properly by individuals with phenylketonuria.
Term
Phenylketonuria (PKU)
Definition
A recessive disorder in humans where the metabolism of phenylalanine produces toxins that can impair mental ability and affect the brain's development, often resulting in death. Babies with PKU can be put on low-phenylalanine diet to avoid this. This mutation also interferes with melanin synthesis; individuals have lighter hair colour. This mutation also results in rare compounds in the blood and urine.
Term
Phocomelia
Definition
A rare dominant disorder where limb development is disrupted. The phenotype for phocomelia is also caused by thalidomide, and example of phenocopy.
Term
Phosphate group
Definition
One of the constituents of a nucleotide. Attaches to the pentose sugar of the neighboring nucleotide. Forms the phosphodiester bond.
Term
Phosphodiester bond
Definition
The bond formed by the phosphate group in a polynucleotide chain. The C3 of one sugar is linked to the C5 of the other sugar.
Term
Piebaldism
Definition
A rare autosomal dominant disorder that shows variable expressivity. The absence of melanocytes in certain areas causes white patches on the skin and/or hair.
Term
Plant height
Definition
One of the seven traits Mendel looked at in sugar snap peas. Plants are either tall or dwarf.
Term
Plasmid
Definition
An independently replicating circular DNA, carrying three to several hundred genes. A bacterium may have as many as eleven in addition to the chromosome. Most are not required for the survival of the cell, but may have an essential gene such as resistance to an antibiotic. Includes F factors, R plasmids, and Col plasmids.
Term
Pleated sheet
Definition

Beta sheet

A secondary structure in proteins. Formed by looping of the polypeptide back on itself, held together with hydrogen bonds.

Term
Pleiotropy
Definition

"To take many turns"

When one gene affects many (seemingly unrelated) aspects of phenotype. The result of complex interactions between biochemical pathways. Examples: PKU, singed mutation, sickle cell disease, cystic fibrosis.

Term
Ploidy (n)
Definition

"Fold"

The number of complete chromosome sets.

Term
Pod colour
Definition
One of the seven traits Mendel looked at in sugar snap peas. Pods are either green or yellow.
Term
Pod shape
Definition
One of the seven traits Mendel looked at in sugar snap peas. Pods are eighter round or constricted.
Term
Polar bodies
Definition
Three are produced from one meiosis event in females. They are aborted. Only the egg survives.
Term
Polydactyly
Definition
A disorder causing the presence of extra fingers and toes. It shows incomplete penetrance: only 50% of individuals with the genotype for polydactyly actually have extra digits.
Term
Polymorphic
Definition
When all the alleles are found at high frequencies in the population.
Term
Polypeptide
Definition
The product of genes. Macromolecules built of linear chains of amino acids. The constituents of proteins.
Term
Polyploid
Definition

"Many fold"

Having more than two copies of the haploid genotype. 30% - 35% of plants are polyploid. Rare in animals because it interferes with sex determination: certain fish and amphibians are polyploid. In plnats, cell size and organism size is increased; the plant produces larger seeds and fruits, and they are often used in agriculture: wheat, coffee, potatoes, bananas, strawberries, cotton, ornamentals. Many polyploids are sterile: chromosomes separate irregularly in meiosis, leading to aneuploidy gametes. Polyploid plants usually reproduce asexually.

Term
Polytene
Definition

"Many threads"

A bundle of chromosomes aligned in parallele. Chromosomes are stuck in interphase. Found in many insect species including mosquitoes and Diptera. In Drosophila the chromosomes pair and form 9 rounds of replication, and form perfect alignments, with all the centromeres converging at the chromocentre. Calvin Bridges studied polytenes in Drosophila.

Term
Population subdivision
Definition
An evolutionary influence that can cause the Hardy Weinberg principle to be false.
Term
Positive supercoiling
Definition
When the DNA is wound right-handedly, in the same direction as the DNA. Some viruses have positively supercoiled DNA.
Term
Primary sturcture
Definition
Structure in proteins. Amino acid sequence.
Term
Prion
Definition
Proteinaceous infective particles. Discovered by Stanley Prusiner. Causes Mad Cow Disease.
Term
Probe
Definition
An isolated DNA sequence labelled with a fluorescent dye. Used in chromosome painting.
Term
Prokaryotic
Definition
Simpler organisms without organelles.
Term
Prometaphase
Definition
Early metaphase. The second phase of mitosis. The nuclear envelop breaks down and fragments. Spindle microtubules attach to kinetochores of sister chromatids. Polar microtubules grow inwards from each spore, but do not attach to sister chromatids.
Term
Promoter region
Definition
A region on a DNA strand where RNA polymerase attaches during the initiation stage of transcription.
Term
Prophage
Definition
A dormant sequence of viral DNA in a bacterial chromosome. The lytic gene is turned off. Mutants in bacteria. Can use this to make bacteria produce novel substances. It can be replicated several times as the cell divides.
Term
Prophase
Definition
The first phase of mitosis. The mitotic spindle becomes organized between two centrosomes and begins to migrate to opposite ends of the cell. Chromosomes continue to condense into visible threads. The nucleolus begins to disappear.
Term
Prophase I
Definition
The first phase of meiosis I. Replicated chromosomes condense. Centrosomes begin to separate to opposite poles. Homologous chromosomes pair. Crossing over takes place. After crossing over, homologous chromsomes move to opposite poles. Chromatids and chiasmata become visible. Nucleolus and nuclear envelope disappear. Spindle microtubules are fully formed and attached to kinetochores of homologs.
Term
Prophase II
Definition
The first phase of meiosis II. Resembles mitotic prophase. Duplicated centrosomes separate and move to opposite poles. Spindle apparatus attach to sister chromatids and move them to the centre of the cell.
Term
Prophase arrest
Definition
In human females, meiosis begins as a fetus and stalls in prophase I for 16 - 40 years. The longer egg cells stay in prophase arrest, the higher the chances of a nondisjunction event. Bivalents with crossovers near the ends of the chromatids are fragile and increasinlgy unstable over time; if a bivalent dissociates, nondisjunction occurs.
Term
Protamine
Definition
Replaces histones in sperm cells.
Term
Protease
Definition
An enzyme that degrades proteins.
Term
Proteins
Definition

"Proteios", of first importance

A biological macromolecule. Made of polypeptides, the product of genes, folded into complex structures. The most complex and abundant macromolecule in cells. Proteins make up most of the dry weight of cells. Have hundreds of functions including: chemical catalyst, defense, regulation, receptors, structural components, storage, movement, and transportation. Have primary, secondary, tertiary, and quaternary structure.

Term
Prototroph
Definition
A wild-tyep E. coli bacteria that can synthesize amino acids, vitamins, purines, and pyrimidines from minimal medium and inorganic salts.
Term
Pseudoautosomal genes
Definition
Genes on both X and Y chromosomes (usually near the ends). Follow autosomal patterns of inheritance.
Term
Punnett square
Definition
A table showing all possible genotyeps of a cross, and their phenotypes. Named after the scientist who devised it.
Term
Purine
Definition
The nitrogen-containing bases adenine and guanine. Double-ringed.
Term
Pyrimidine
Definition
The nitrogen-containing bases cytosine, thymine, and uracil. Single-ringed.
Term
Q arm
Definition
The short arm of a chromosome.
Term
Quaternary structure
Definition
Structure in proteins. Two or more polypeptides interacting. Hemoglobin and collagen have quaternary structure.
Term
Queen Victoria of Great Britain
Definition
A carrier of haemophilia. Passed it into the Russian Imperial family.
Term
Quinacrine
Definition
A stain used in cytogenetics. Chromosomes show characteristic patterns of bright and dark bands when exposed to ultraviolet light. Banding is specific to each chromosome.
Term
R plasmid
Definition

Resistant plasmid

A plasmid that makes the host cell resistant to antibiotic drugs. May enable conjugation (plays a role in the spread of resistant bacteria). Can pass to other species of bacteria.

Term
Rare autosomal genes
Definition
Individuals that mate into pedigrees for rare traits are assumed to not be carriers of the trait, unles there is evidence to the contrary.
Term
Receptor
Definition
One of the functions of proteins. Chemicals bind to receptors in nerve cell membranes.
Term
Recessive allele
Definition
An allele where the phenotype shows only in homozygotes.
Term
Recessive epistasis
Definition

Epistasis where the homozygous recessive genotype is epistatic over the hypostatic gene. It doesn't mater what the B genotype is when the A genotype is aa. Produces a 9:3:4 ratio from a dihybrid cross.

aaB_ and aabb both produce the same phenotype

Term
Recessive lethal allele
Definition
Lethal alleles where only homozygotes die. Recessive lethal mutations can linger in populations, since carriers do not die and may pass on the allele. Alleles that cause death before birth can be detected by unusual segregation ratios of 2:1, due to one quarter of progeny aborting. Examples: yellow-lethal in mice, Manx in cats, and Tay Sachs in humans.
Term
Recessive mutation
Definition
A mutation which is recessive. Includes null and hypomorphic alleles. They are easier to detect if they are on sex chromosomes.
Term
Recipient cell
Definition
The bacterium which accepts DNA from the donor cell in recombination in bacteria. Becomes a partial diploid with a linear piece of chromosome, then a double cross-over incorporates the DNA into the circular recipient DNA. A single cross-over creates an unstable linear DNA.
Term
Reciprocal translocation
Definition
A translocation where two pieces are interchanged without any loss of genetic material. During meiosis in translocation heterozygotes, non-homologous chromosomes pair in cruciform pairing.
Term
Recombination
Definition
The separation of linked genes during segregation. The result of crossing-over. Crossover points occur at chiasmata. Allows favourable alleles of different genes to come together in the same organism for increased evolutionary survival.
Term
Recombinants
Definition
Progeny resulted from crossing-over.
Term
Recombination frequency
Definition
The frequency of recombinants. Used to measure the intensity of linkage between genes. Genes more tightly linked recombine less frequently. Recombinataaion frequency can never exceed 0.5. When genes are more than 50 cM distant, the recombination frequency no longer reflects gene distance.
Term
Red blood cell
Definition
Millions are produced in bone marrow to replace old worn out red blood cells. Life span of 3 - 4 months.
Term
Regulatory
Definition
One of the functions of proteins. Control gene expression, co-ordinate cellular activities.
Term
Renaturation
Definition
Slow cooling of denatured DNA. Complementary strands find each other and reform. Rate of renaturation is directly proportional to the copy number of the sequence in the genome. Receptive sequences renature faster.
Term
Repetitive DNA
Definition
When a sequence is repeated as many as a million times, and does not encode proteins. 15% - 80% of eukaryote genomes are repetitive.
Term
Replicate
Definition
The genotypic function of the genetic material. Stores genetic information and accurately transmits it from parent to offspring.
Term
Repulsion
Definition

Trans configuration

"Opposite side"

Ab/aB

A linkage phase. When one dominant allele and one recessive allele are inherited from each parent.

Term
Ribose
Definition
The pentose sugar found in the nucleotides of RNA.
Term
Ribosomal RNA (rRNA)
Definition
A type of RNA. A component of ribosomes.
Term
Ribosomes
Definition
Organelles which translate mRNA into polypeptides. In the cytoplasm. rRNA is a component. Composed of the small and large subunits. tRNAs first bind to the "P" site, then move to the "A" site, depositing their amino acid into the RNA sequence.
Term
Richard Sia and Martin Dawson
Definition
In 1931, showed that the transformation of Streptococcus pneumoniae that Frederick Griffith observed was not mediated by the living mouse host.
Term
RNA
Definition

Ribonucleic acid

A nucleic acid. Stores the genetic information of some viruses. Contains ribose sugar, and the nitrogen-containign bases adenine, guanine, cytosine, and uracil. Single-stranded. DNA is transcribed into RNA, then introns are removed and exons spliced together. Includes ribosomal RNA, messenger RNA, and transfer RNA.

Term
RNA polymerase
Definition
The enzyme which transcribes RAN from DNA.
Term
RNase
Definition

Ribonuclease

An enzyme that degrades RNA.

Term
Robertsonian translolocation
Definition
Non-homologous chromosomes fuse at the centromeres. Named after F.W. Robertson. If two acrocentric chromosomes fuse, it produces a metracentric chromosome, and the short arms fuse and are lost. This type of fusion has occurred often in evolution. Human chromosome 2 is a result of a Robsertonian translocation between two acrocentric chromosomes in great apes. Rare, and even rarer to survive it.
Term
Rolling-circle replication
Definition
The type of DNA replication in conjugation. The DNA "rolls" during replication: one strand of the chromosome is synthesized in the donor cell, and then transferred through the conjugation bridge to the recipient cell, where it is completed.
Term
Rosalind Franklin
Definition
Made essential contributions to the discovery of the structure of DNA, but was not recognized until after her death.
Term
R.P. Donahue
Definition
In 1968, demonstrated that the Duffy blood group locus is on chromosome 1, by discovering a variant that created a chromosome 1 that was longer than usual.
Term
Rye
Definition

Secale cereal

2n = 14

Low protein, high lysine, and does well in poor soils. Crossed with wheat to produce triticale.

Term
S phase
Definition
The second phase of interphase. The characteristic phase of interpahse. The cell's DNA is replicated.
Term
Salmonella typhimurium
Definition
The bacteria in which transduction was discovered by Joshua Lederberg and Norton Zinder.
Term
Satellite bands
Definition
When DNA has a composition of G/C or A/T that is significantly different from 50%, it forms a separate badn when DNA is centrifuged in CsCl. The DNA in these bands is satellite DNA.
Term
Satellite DNA
Definition
DNA found in satellite bands. Is either G/C rich or A/T rich.
Term
Scaffold
Definition

Central core

A structure at the centre of the metaphase chromosome. Composed of non-histone chromosomal proteins.

Term
Scrapie
Definition
Mad Cow Disease when it infects sheep or goats. One symptom is excessive scratching. The animal may scratch off all their wool or hair.
Term
Secondary structure
Definition
Structure in proteins. Either heilical or pleated sheets.
Term
Seed colour
Definition
One of the seven traits that Mendel looked at in sugar snap peas. Seeds are eighter green or yellow.
Term
Seed shape
Definition
One of the seven traits that Mendel looked at in sugar snap peas. Seeds are either round or wrinkled.
Term
Selective medium
Definition
Medium containing drugs, or lacking metabolites, in order to phenotype bacteria as mutants or wild-types.
Term
Selman Waksman
Definition
A Ukrainian immigrant in the US who discovered streptomycin, an antibiotic, in 1943. First cured tuberculosis with antibiotics in 1944.
Term
Semi-dominance
Definition

Incomplete dominance where the heterozygote has a mid-way phenotype of the dominant and recessive.

Example: colour in snapdragons.

AA = red

Aa = pink

aa = white

Term
Serratia marcescens
Definition
A bacteria that produces a red pigment which results in distinctive red colonies.
Term
Sewal Wright
Definition
Measured the intensity of inbreeding in 1921. Invented the inbreeding coefficient.
Term
Sex chromosome
Definition

Discovered by C.E. McLung, N.M. Stevens, W.S. Sutton, and E.B. Wilson. Present in unequal numbers in males and females.

Humand have 1 pair: the X and Y chromosomes.

XX = female

XY = male

Term
Sex determination
Definition

In some species, the environment determines sex (in one species of turtle, it is temperature).

In humans and other placental animals, it is determined by the presence of a Y chromosome.

In Drosophila, sex is determined by the ratio of X chromosomes to sets of autosomes (there are 3 autosomes): a ratio of 1.0 or greater leads to females, a ratio of 0.5 or less leads to males, and a ratio between 0.5 and 1.0 leads to intersex flies.

In birds, ZW leads to a female, and ZZ leads to a male.

Sex determination in honeybees and some wasps is based on the haplo-diplo system.

In Bracon hebetor, sex is determined by the genotype at a certain locus.

Term
Sexual dimorphism
Definition
When males and females have conspicuously different phenotype.
Term
Shelterin
Definition
Six proteins which bind to specific telomere sequences, and protect the t-loop from degradation and modification.
Term
Shibire
Definition

"Paralysis"

A temperature-dependent mutation in Drosophila that cause the flies to be sensitive to shocks: they become paralyzed with fear of their cage is shaken. Above 29ºC, they all become parlayzed and it can be fatal.

Term
Shigella species
Definition
Bacteria species which cause dysentery. Includes S. dysenteriae, S. flexneri, S. boydii, and S. sonnei. Frequency of drug resistant straints increased 59% in the sewers.
Term
Siamese
Definition
A temperature-sensitive mutation in cat. An allele of the Tyrosinase gene. The protein produced is inactivated at higher temperatures near the cat's body core, causing a light brown to white fur colour. At the tips of the extremities (ears, face, legs, tail), the enzyme is activated by the cooler temperature, and produces pigment, causing the characteristic dark areas on a Siamese cat.
Term
Sickle cell anemia
Definition
A disorder that shows pleiotripy. It causes resperatory problems, sickled blood cells, chronic infections, joint pain, enlarged spleen, and stroke.
Term
Side group
Definition
A component of an amino acid. It is attached to the central carbon. There are 20 different possible side groups, making 20 different amino acids.
Term
Singed
Definition
A mutation in Drosophila that shows pleiotropy. It causes short, twisted bristles on the body, and females are sterile and produce flimsy, ill-formed eggs.
Term
Sister chromatids
Definition
Identical DNA strands, held together in the chromosome at the centromere. Have kinetochores at the centre. Become the chromosome of the daughter cell.
Term
Soft red winter wheat
Definition
A variety of bread wheat used to make cake and pastry flour.
Term
Soft white wheat
Definition
A variety of bread wheat used to make pastry flour.
Term
Solenoid model
Definition
A model for how DNA is packaged into chromatin fibres.
Term
Specialized transduction
Definition
Transduction where a recombination event occurs between the host and the viral DNA, producing a sequence that contains a piece of mixed bacterial and viral DNA that is packaged into progeny phages. Occurs only for genes adjacent to the prophage. The lytic genes are not present, excepting in Lft lysates, and as such the progeny phages cannot become lytic in their hosts without a wild-type "helper" phage.
Term
Sperm
Definition
500 million are produced per day of males of reproductive age. Four sperm cells are produced from each meiotic event.
Term
Split hand-foot syndrome
Definition
A rare autosomal dominant disorder that shows variable expressivity. A deficiency or absence of one or more central digits of the hand or foot. Individuals with identical genotype for this disorder have a wide range of hand and foot structures.
Term
SRY (sex-determining region Y)
Definition
A gene on the Y chromosome, just outside the psuedoautosomal region. Codes for testis-determining factor (TDF). If it is absent, it can lead to XY females. If it is found on the X chromosome, it can lead to XX males.
Term
Stanley Prusiner
Definition
Discovered prions in 1982.
Term
Sterile mutation
Definition
A mutation that limits reproduction. Some affect both sexes, but most affect only males or females. Can be dominant or recessive. Some completely prevent reproduction, others just impair it.
Term
Stop codon
Definition
A codon in the mRNA that causes the ribosome subunits to separate during the termination phase of translation.
Term
Stop signal
Definition
A DNA sequence that causes RNA polymerase to detach from the DNA strand during termination phase of transcription.
Term
Storage
Definition
One of the functions of proteins. Reserves food. Includes ovalbumin in egg whites and zein granules in corn seeds.
Term
Streptococcus pneumoniae
Definition
The bacteria which causes pneumonia in mammals. In 1928, Frederick Griffith discovered transformation in this bacteria. It will take up DNA from any source.
Term
Structural
Definition
One of the functions of proteins. Support and reinforcement. Includes collagen and elastin.
Term
Sugar snap peas
Definition

Pisum sativum

A common garden plant. There are many varieties. Mendel used them in his experiments. Mendel noticed that certain characteristics of peas were passed from generation to generation. Flowers are self-fertilizing because they are tightly closed; doesn't allow in foreign pollen, making it easy to control parentage of offspring. Mendel performed cross-fertilization by hand pollination. Fertilizing organs are behind the keel petal. Mendel looked at seven traits of the sugar snap pea: flower colour, seed colour, seed shape, pod colour, pod shape, flower position, and plant height.

Term
Summer squash
Definition
A plant which shows epistasis in fruit colour. A squash homozygous recessive for C has a white fruit, but if one or more dominant allele is present, colour is determined by G. GG or Gg squash are yellow, and gg squash are green. C produces a protein that blocks synthesis of yellow pigment. G produces a protein that blocks conversion of yellow pigment into green pigment. A dihybrid cross produces a 12:3:1 ratio.
Term
Supercoiling
Definition
Tight compaction of functional DNA. One end is held still while the other end is twisted. In linear DNA, the ends are held to protein components of the chromosome. Includes positive and negative supercoils.
Term
Susumu Ohno
Definition
In 1960, proposed that the darkly staining mass discovered by Murray Barr and Ewart Bertram (the Barr body), was the X chromosome.
Term
t-loop
Definition
The guanine-rich 3' overhang of the telomere loops back and binds with a complementary sequence. It is protected by shelterin from degradation and modification.
Term
Tay Sachs
Definition
A recessive lethal allele in humans. Affected individuals often die before the age of 3. It has an allele frequency of 0.017 in the general population.
Term
Telomeres
Definition
The termini of DNA strands. Have their own replication apparatus, separate from DNA. Have repetitive DNA sequences, which is highly conserved in vertebrates, ranging from 500 - 300 bp, reducing with the age of the organism. In Drosophila, the telomere is a transposable element. There is a guanine-rich 3' strand overhang. In humans and other species, it folds back to make a t-loop. Prevents fusion of chromosomes and facilitates replicationo f the ends of lienar DNA moleucles.
Term
Telophase
Definition
The fifth phase of mitosis. Daughter chromosomes comlete migration to separate poles. The nuclear envlop reforms around the chromosomes of each new daughter cell. The contractile ring forms. Chromosomes decondense into threadlike filaments.
Term
Telophase I
Definition
The fourth phase of meiosis I. A new nuclear envelop forms around the separated chromosomes. Cytokinesis is almost complete. The contractile ring pinches the cell in two.
Term
Telophase II
Definition
The fourth phase of meiosis II. Chromosomes reach their poles and begin to uncoil. The nuclear envelop reforms, and cytokinesis is completed.
Term
Temperate bacteriophage
Definition
Can either kill its host, or enter association with the host to replicate its genome along with the host cell's genome during cell division. Example: bacteriophage lambda.
Term
Temperature sensitive mutation
Definition
Mutations that occur only at certain temperatures. Example: Himalayan coat colour in rabbits, Siamese coat colour in cats, and Shhibire mutation in Drosophila.
Term
Termination (transcription)
Definition
The third stage of transcription. RNA polymerase encounters a stop signal on the DNA sequence and separates from the DNA strand.
Term
Termination (translation)
Definition
The third stage of translation. A stop codon is encountered and a release factor binds to the stop codon. The ribosome separates into its two subunits and the mRNA is released.
Term
Tertiary structure
Definition
Structure in proteins. The final 3D shape of a polypeptide with its secondary structures. Interactions include disulfide bonds, hydrogen bonds, ionic bonds, and Van der Waals forces.
Term
Testicular feminization
Definition
When the testosterone signalling system fails, caused by a mutation in Tfm. The organism develops as a female even after development of tesis, and is sterile.
Term
Testis-determining factor (TDF)
Definition
A protein coded by the SRY gene on the Y chromosome. Causes development of testis in early embryonic development.
Term
Testosterone
Definition
A hormone more abundant in males than females. It is secreted by the testes, leading to development of secondary male characteristics. It interacts with the gene for pattern baldness.
Term
Tetrad
Definition
A grouping of four chromatids that forms during crossing-over.
Term
Tetraploid (4n)
Definition

"Four fold"

Having four copies of the haploid genome. Usually sterile due to uncertainties in meiosis. A fertile allotetraploid is an amphidiploid.

Term
Tfm
Definition
An autosomal gene that codes for testosterone receptor. A mutation in these gene causes failure of the testosterone signalling system, leading to testicular feminization. This mutation is transmitted from the mother, since male individuals with the mutation are sterile.
Term
Thalidomide
Definition
An example of phenocopy. Medication that treats morning sickness in pregnant women also causes the infant to show the phenotype of a rare dominant disorder, phocomelia. Thalidomide has now been banned for many years.
Term
Thomas Hunt Morgan
Definition
A geneticist. The husband of Lillian Morgan. In 1909, he discovered a mutation in eye colour of Drosophila that had different phenotypic ratios between males and females. Hypothesized that the gene was on a sex chromosome; this was proved by Calvin Bridges. Postulated the Chromosome Theory of Heredity. His students created a map of the Drosophila X chromosome.
Term
Thymine (T)
Definition
A nitrogen-containing base found in DNA. Pairs with adenine with two hydrogen bonds. A pyrimidine: one ring with two =O groups and one CH3 group. Its nucleotide is dTMP.
Term
Tobacco mosaic virus (TMV)
Definition
A virus that was used in the experiment by Heinz Frankel-Contrat and coworkers to show that RNA was the genetic material in some viruses.
Term
Tightly linked genes
Definition
Produce 2 classes of offspring as though the probability of recombination was 0. Produces a 3:1 ratio.
Term
Tortoiseshell cat
Definition

Calico cat

A coat colour patterning found in female cats heterozygous on the X-linked trait for coat colour. The cat is a genetic mosiac; half of the cat's cells have the gene for orange fur inactivated, and half have the gene for black inactivated. This results in random patches of black and orange on the cat.

Term
Transcription
Definition
The process by which DNA is turned into RNA. RNA polymerase attaches to the promoter region of DNA, and transcribes an RNA strand.
Term
Transducing particles
Definition
Bacteriophages containing bacterial DNA in transduction.
Term
Transduction
Definition
A parasexual process. Requires no cell contact. Not sensitive to DNase. The only parasexual process which can occur in all types of bacteria. Discovred by Norton Zinder and Joshua Lederberg. Bacterial DNA is carried form one bacterium to anther by a transducing particle bacteriophage. Two types: generalized transduction and specialized transduction.
Term
Transfection experiment
Definition
A protoplast is infected with pure viral DNA. Proves that the genetic material is DNA.
Term
Transfer RNA (tRNA)
Definition
A type of RNA. Clover-leaf shaped molecules that carry amino acids on one end, and have anticodons on the other. Transfer amino acids to the ribosome complex during translation.
Term
Transformation
Definition
A parasexual process. Discovered by Frederick Griffith. Requires no cell contact. Sensitive to DNase. Uptake of free DNA released from the donor cell. The sequence is then incorporated into the recipient cell's chromosome, forming a heteroduplex. Frequency of two genes being transformed together is a function of their distance on the chromosome. E. coli does not have transformation. Observed in Streptococcus pneumoniae, Bacillus subtilis, Haemophilus influenza, and Neisseria gonorrhea.
Term
Translation
Definition
The process by which mRNA is turned into polypeptides. Ribosomes translate mRNA. tRNA donates amino acids based on the sequence of codons. Includes the initiation stage, elongation stage, and termination stage.
Term
Translocation
Definition
A chromosome rearrangement where a transposable element is detached and fuses with another, non-homologous chromosome. Includes reciprocal translocations and Robertsonian translocations.
Term
Translocation heterozygote
Definition
A cell where one chromosome has had a reciprocal translocation and the other has not. During meiosis, these chromosomes pair with cruciform pairing.
Term
Translocation homozygote
Definition
A cell where both chromosomes have had a reciprocal translocation.
Term
Transport
Definition
One of the functions of proteins. Carry molecules and ions. Includes hemoglobin, which carries oxygen, and glucose transporter, which carries glucose.
Term
Transposable elemen
Definition
Term
Transposable genetic element
Definition
A DNA sequence that can change location within a chromosome, or to another chromosome, in chromosome rearrangements. 40% - 50% of the human genome is transposable genetic elements. 80% of the corn genome is transposable genetic elements.
Term
Triplo-X syndrome
Definition

47, XXX

Individuals survive because two of the X chromosomes in each cell are inactivated with a Barr body. Phenotypically normal females, with slight mental impairment and reduced fertility.

Term
Triploid (3n)
Definition

"Three fold"

Having three sets of chromosomes. When meiosis occurs in a triploid individual, there are two possibilities in metaphase I: one bivalent and one univalent, or one trivalent and one cell with no chromosome. Some varieties of seedless citrus, bananas, seedless grapes, and seedles watermelon are triploid.

Term
Trisomy
Definition
Hyperploidy where there are three copies of one chromosome. In plants it is primarily passed down by the female parent because aneuploid pollen do not compete well. In humans only the autosomal trisomies that result in live births are Down syndrome, Patau syndrome, and Edwards syndrome.
Term
Triticale
Definition
A cross between rye and emmer wheat, first produced by a 3n = 21 plant, which was sterile, then chromosomes were doubled to produce 6n = 42 allohexaploid. Has the high protein content of wheat and the lysine content of rye, and is hardy in poor soil conditions.
Term
Trivalent
Definition
Three homologous chromosomes "paired" together in metaphase I. May occur in meiosis of triploid organisms.
Term
ts mutants
Definition
Mutants of bacteriophage T4 that are temperature sensitive and cannot grow at 42ºC.
Term
Tuberculosis (TB)
Definition

Mycobacterium tuberculosis

A bacterial disease. Highly contagious, transmitted by aerosolized droplets from coughs and sneezes. Often fatal; there was no effective treatment in the past, and families with TB often lived in isolation. A drug-resistant strain arose in a New York prison in 1991, killing 13 inmates and one guard. There are many straings of drug-resistant TB: MDR and XDR. 2 million people die from tuberculosis each year. In some parts of the world, people cannot be effectively treated with antibiotics.

Term
Turner syndrome
Definition

45, X

Caused by an XO genotype. Occurs in 1/2,500 female births. First described by Henry H. Turner in 1938. Individuals are female and sterile: ovaries fail to develop, uterus and oviducts can be small and immature, retarded sexual development, short stature, webbing of the skin in the neck, cardiovascular abnormalities, and hearing impairment. There are no Barr bodies. Recieve growth hormone therapy to increase stature, receive estrogen at puberty. Caused by fertilization of a gamete that lacked a sex chromosome, or from loss of a sex chromosome in mitosis early after fertilization. Some individuals may be a genetic mosaic for Turner syndrome, leading to reduced symptoms.

Term
Type A blood
Definition

IAIA or IAi

Acetylgalactosamine is present on the surface of red blood cells. 41% of the population have this blood type.

Term
Type AB blood
Definition

IAIB

Acetylgalactosamine and galactose are both present on the surface of red blood cells. 4% of the population have this blood type.

Term
Type B blood
Definition

IBIB or IBi

Galactose is present on the surface of red blood cells. 11% of the population has this blood type. Linked to Nail-Patella syndrome.

Term
Type O blood
Definition

ii

Neither acetylgalactosamine nor galactose are present on the surface of red blood cells. 44% of the population has this blood type.

Term
U-tube experiment
Definition
Tests whether or not cell contact is required for DNA to transfer in a parasexual process. Two arms are separated by a glass filter that may allow DNA and viruses to pass, but not bacteria.
Term
Unequal survival
Definition
An evolutionary influence that can cause the Hardy Weinberg principle to be false.
Term
Unidirectional
Definition
Passes in one direction: not reciprocal. Recombination in bacteria is unidirectional, from the donor cell to the recipient cell.
Term
Unineme model
Definition

Single-strand model

One strand of DNA extends through the chromosome. Considerable evidence supports this model.

Term
Univalent
Definition
A chromosome without a homologous partner in metaphse I. May occur in meiosis of triploid organisms.
Term
Upland cotton
Definition
90% of cotton varieties. Produced form a cross between Old World cotton and American cotton over a million years ago; this produced a 2n = 26 plant, which was sterile, the chromosomes were then doubled to produce a 4n = 52 amphidiploid.
Term
Uracil (U)
Definition
A nitrogen-containing base found in RNA. A pyrimidine. Pairs with adenine with three hydrogen bonds.
Term
Van der Waals forces
Definition
Non-covalent interactions that help form tertiary structure in proteins.
Term
Variable expressivity
Definition
Individuals with identical known genotypes have a range of phenotypes. Example: lobe eye mutation in Drosophila.
Term
Virulent bacteriophage
Definition
Uses machinery of the host cell to produce progeny viruses, killing the host in the process. Example: bacteriophage T4.
Term
Virus
Definition
May be considered a living thing. May be purified and crystalized. Only utilize energy and reproduce if introduced to cells of their host. Include bacteriophages.
Term
Visible mutation
Definition
A mutation that changes an aspect of morphology. Most are recessive. Geneticists have learned much about genes from visible mutations.
Term
W. Waldeyer
Definition
A German cytologist who discovered chromosomes.
Term
Wild barley
Definition

Triticum aegilops

Crossed with wild einkorn to produce emmer wheat.

Term
Wild einkorn
Definition

Triticum monococcum

Crossed with wild barley to produce emmer wheat.

Term
Wild type allele
Definition
The allele which is most common in wild populations. Often symbolized by +. A functional protein is produced. Often the most dominant allele in an allelic series.
Term
William Astbury
Definition
In 1947, used X-ray diffraction to show that DNA is a stacked polymer of bases.
Term
William Bateson and R.C. Punnett
Definition

Bateson published Mendel's Principles of Heredity in 1909.

The two performed experiments producing the first evidence of linkage. Crossed varieties of sweet peas and found that genes for flower colour and pollen shape were linked together; produced significantly more paternal classes than non-parental classes.

Term
X chromosome
Definition
A sex chromosome. Females have two. Males have one. It is necessary for viability. Zygotes without an X chromosome die immediately. Two chromosomes are necessary for fertility in females. There are over 1000 genes on the human X chromosome.
Term
X-linked dominant trait
Definition
Affected males always produce affected daughters, but normal sons. Affected females always produce affected children.
Term
X-linked recessive trait
Definition
Carrier females can produce affected sons and normal sons. Affected females always have affected fathers and carrier mothers. More commonly affects males.
Term
XO
Definition

The male genotype in some species.

In Drosophila, this genotype can arise from fertilization of a nullo-X egg with an X-chromosome containing sperm; such males are sterile.

In humans, this genotype produces a female with Turner syndrome.

Term
XX
Definition
The female genotype. Males can occur with this genotype, if SRY is found on one of the X chromosomes.
Term
XXX
Definition
The genotype for triplo-X syndrome. In placental mammals, two X chromosomes are inactivated.
Term
XXX metafemale
Definition
In Drosophila, a result of fertilizaiton of a diplo-X egg with a X chromosome-containing sperm. Weak and sickly, with anatomical abnormalities: ragged wings, etched abdomens.
Term
XXY
Definition

In Drosophila, a result of fertilization of a diplo-X egg with a Y chromosome-containing sperm: produces phenotyically normal females, but produces a higher amount of nondisjunction events in meiosis.

In humans, this genotype produces a male with Klinefelter syndrome.

Term
XY
Definition
The male genotype for some species, including humans. Females can occur with this genotype if SRY is absent from the Y chromosome.
Term
XYY
Definition
In humans, this genotype produces a male who tends to be tall.
Term
Y chromosome
Definition
A sex chromosome. In Drosophila, the Y chromosome does not determine sex, but is necessary for male fertility. In humans and other placental mammals, its presence leads to a male individual. In humans, the Y chromosome is much shorter than the X chromosome, and is acrocentric. Sperm cells containing Y chromosomes are slightly ligher and faster than those with X chromosomes, so the frequency of male zygotes and births is slightly higher than that of females, but reduced viability in males evens out the frequency by reproductive age. There are about 300 genes on the human Y chromosome, but fewer than 100 are functional; mostly repetitive, non-coding DNA.
Term
Y-linked traits
Definition
Traits on the Y chromosome. Mutations on the Y-chromosome often lead to male sterility, thus are never tansmitted.
Term
Yellow-lethal mutation
Definition

A recessive lethal mutation in mice that also affects coat colour. A dihybrid cross would result in a 2:1 ratio, since one quarter of offspring die before birth.

A+A+ = agouti mouse

AYA+ = yellow mous

AYAY = lethal

Term
YO male
Definition
In Drosophila, a result of fertilization of a nullo-X egg with a Y-chromosome contianing sperm. It dies immediately.
Term
Zigzag model
Definition
A model for how DNA packages into chromatin fibres. Found in frozen chromosomes.
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