Diploid

cell or organism constiting of two sets of chromosomes--usually one from mother, one from father

genes come in pairs

one gene, two copies

Alleles

different forms of a gene

'A' and 'a' are different alleles

gametes are (haploid or diploid)

haploid

Mendel's law of segragation

members of a gene pair segregate equally into gametes which are haploid

each gamete received ONE COPY of gene

synonym for heterozygote

hybrid

genotype

genetic constitution of trait under study

phenotype

outward manifestation of underlying genotype

Autosome

chromosome that is not a sex chromosome

PKU

phenylketonuria

autosomal recessive disorder

deficient in the hepatic enzyme phenylalanine hydroxylase

 body cannot properly process a.a. phenylalanine

which accumulates and then gets converted to phenylpyruvic acid (phenylketone)which can lead to brain damage

phenylalanine hydroxylase

hepatic enzyme

individs suffering from autosomal recessive disorder PKU are deficient in this enzyme

which metabolizes a.a. phenylalanine into tyrosine

phenylpyruvic acid

phenylketone

accumulates in people suffering from PKU

(defficient in enzyme phenylalanine hydroxylase, which converts phenylalanine to tyrosine)

accumulation interferes with development of nervous system--leads to brain damage

name three autosomal recessive disorders

1. PKU

2. albinism

3. cystic fibrosis

albinism

autosomal recessive disorder

lacking melanin pigment

cystic fibrosis

autosomal recessive disorder

lack of chloride channel important in creating sweat, digestive juices, and mucus;

results in excess mucus production

x-linked recessive

affects who more often

what gener are the carriers

example

affects males more often

women are the carriers

example: hemophilia

two methods by which males can be afflicted with hemophilia

inherit recessive allele from mother

new mutation

hemophilia

don't have normal clotting factor levels which interfered with fibrin formation--necessary to maintain the initial clot

don't bleed more, bleed longer

very dangerous if injury occurs in areas of brain or inside joints

recessive mutations are generally

what type of loss of function alleles (?morphic)

haplosufficient or -insufficient?

heterozygote has what type of phenotype

amorphic (null) or hypomorphic (leaky) loss of function alleles

haplosufficient gene

heterozygote with wild type phenotype

haplosufficient

one copy of the gene is enough for function

dominant mutations are generally

?morphic

haplosufficient / insufficient?

heterozygote has what phenotype?

antimorphic, hypermorphic, neomorphic

in a haploinsufficient gene

heterozygote has a mutant phenotype

haploinsufficient

one copy of the gene is not enough for wt phenotype

antimorphic mutations

definition

also called

loss of function but in addition gene product has negative effect on the wild type gene product

dominant negative

dominant negative mutations

example

also called antimorphic mutations

usually occurs if the mutatnt product can still interact with the same elements as the wt product, but block some aspect of its function.

example: truncated receptors missing intracellular domain; form inactive heterodimers with wt receptors or compete with wt receptors for ligand binding

hypermorphic mutations

gain of function

more activity

neomorphic mutations

example

gain of function, but a novel gene activity is produced

Antennapedia: neomorphic mutation causing ectopic expression of leg determining gene where antennae are supposed to be

give two gain of function dominant mutations

tell difference between them

hypermorphic mutations (more gene activity)

neomorphic (novel activity produced)

clue for identifying autosomal dominant disorders

phenotype tends to appear in every generation of the pedigree

pseudoachondroplasia

caused by mutations in what gene

gene function

where is protein product of gene normally found

what happens in mutated gene

dwarfism: autosomal dominant disorder of bone growth

mutations in COMP gene

COMP protein essential for normal development of cartilage and its conversion to bone

usually found in spaces betwn chrondocytes

abnormal prot stuck in cell-where it builds up and kills chondrocyte

early death of chondrocyte prevents normal bone growth causes short stature

COMP gene

mutations in this gene cause what

and how

pseudoachondroplasia

COMP protein stuck in cell, kills chondrocyte

chondrocyte

cartilage forming cells

achondroplasia

what type of disorder

afflicted gene

normal gene function

mutant gene activity

autosomal dominant disorder

cartilage never converted to bone

FGFR-3  = fibroblast growth factor receptor 3

FGFR3 has a negative regulatory effect on bone growth--limits formation of bone from cartilage partic in long bones

mutated form of receptor is constitutively active

leads to severely shorted bones

give three examples of autosomal dominant disorders

1. pseudoachondroplasia

2. achondroplasia

3. FOP

are achondroplasiacs heterozygous or homozygous?

heterozygous

two copies of mutant gene are fatal before or shortly after birth

how does achondroplasia mutation arise?

7 out of 8 achondroplasia mutations arise de novo

spontaneous mutation in gene

FOP

mutated gene

normal gene function

mutated gene activity

autosomal dominant

fibrodysplasia ossificans progressiva

muscle tissue and connective tissue are gradually ossified; overgrowth of bone and cartilage and fusion of joints

results in extraskeletal or heterotopic bones

ACVR1 gene encodes a BMP--bone morphogenic protein type 1 receptor

protein helps control growth and devel of bones and muscles-including ossification

mutation causes constitutive activation

what is early sign that children have FOP

congenital malformations of great toe

how do most cases of FOP arise

de novo

although a small number of cases are inherited

X-linked dominant

affected males pass only to

example

daughters

Coffin-Lowry syndrome

Coffin-Lowry syndrome

mutation in what gene

normal gene activity

different affects males females

x-linked dominant

mutations in RPS6KA3

mutation causes little or no RPS6KA3 protein

males have severe to profound intellectual disability and delayed development

affected females may be cognitively normal or may have intellectual disbaility ranging from mild to profound

RPS6KA3

what are substrates of protein product?

mutation in this gene causes Coffin-Lowry syndrome

which normally encodes a kinase involved in cell signalling pathways required for learning, formation of long term memory, survival of nerve cells

phosphorylates substrates like CREB and histone H3

one chromosome pair = two  ____

homologs

mitosis

what do you start with what do you end with

two stages

start with 1 cell

end with 2 identical to first

two stages: replication (interphase) and segregation (metaphase, anaphase, telophase)

in anaphase sister chromatids are pulled apart

meiosis

what do you start with what do you end with

four stages

special steps

used for formation of gametes

start with one diploid cell, end with four haploid cells, each containing half the genetic material of parent cell

four stages: 1. replication 2. pairing 3. segregation 4. segregation

*metaphase I: pairing of homologs; 4 chromatids--tetrad

*anaphase I: centromeres do not split --homologous pairs split

two special features regarding meiosis

1. pairing of homologs

4 chromatids = tetrad

Does not occur in mitosis

2. centromeres do not split in meiosis I

--homologous pairs are seperated

Mendel's law of independent assortment

what is it

when does it occur

each homologous pair arranges itself independently of others

anaphase I of meiosis

independent assortment between unlinked genes leads to

what leads to recombination

in linked genes

in unlinked genes

in linked genes: crossing over

in unlinked genes: independent assortment

numbers of cross overs

and thus the number of recombinants

depends on

distance between two genes on chromosome

1 map unit =

locus

Drosophila nomenclature

genes named how

wt designated how

genes in upp case vs lower case

genes often names by mutant phenotype they exhibit

wt deginated with ⁺

genes in upper case = dominant muts

lower case = recessive muts

point mutations induced by mutagens that cause

what, in DNA sequence

and what, in amino acid sequence

DNA sequence:

tranitions

transversions

indels

Amino acid sequence:

missense

nonsense

frameshift

Transition point mutation

when one purine subbed for the other purine

or

when one pyrimidine subbed for the other pyrimidine

Transversion point mutation

when correct purine replaced by a pyrimidine

or

when correct pyrimidine replaced by purine

transversion consequences are more severe, less common

indel point mutations

insertion or deletion of a base

missense

possible result of point mutation

codon specifies different amino acid

nonsense

possible result of point mutation

codon signals chain termination--stop codon

frameshift

possible result of point mutation

one base pair addition or deletion

three types of chromosome mutations

relocation of genetic material

loss of genetic material

gain of genetic material

relocation of genetic material

(chromosome mutations)

two examples

translocation

(from another chromosome)

inversion

gain of genetic material

(chromosome mutations)

two examples

extra chromosomes

duplication

aneuploidy

caused by what what

three examples

abnormal number of chromosomes

nondisjuction in meiosis

xo

xxy

trisomy 21

mis-segregation

what it is

what is result

results when it occurs in meiosis I

meiosis II

nondisjunction in meiosis

aneuploidy

meiosis I:

four daughter cells

2 n+1 and 2 n-1

meiosis II:

2 n; 1 n+1; 1 n-1

when nondisjunction occurs in mitosis, what is result

loss of heterozygosity

reciprocal translocation

example

result

philadelphia chromosome (between chroms 9 and 22) causes chronic myelogenous leukemia

Bcr1-Abl fusion protein

encoded on what chromosome

how does that chromosome arise

what does fusion protein do

what illness results

encoded by Philadelphia chromosome

(result of reciprocal translocation between chromosome 22 and chromosome 9)

c-abl gene on chromosome 9 encodes a kinase

hybrid mRNA makes fusion protein which is always active--activates cell cycle proteins

causes Chronic myelogenous leukemia

inversion heterozygotes form what structures during homolog pairing

and what is the result

inversion loops

crossing over in loops lead to inviable meiotic products

balancer chromosomes

what do they do

how

why useful

genetic tool used to prevent crossing over between homologous chromosomes during tetrad formation during meiosis

they have multiple inversions along chromosome so that homologue pairing is disrupted (This is when crossing over usually occurs)

if there is a crossover, progeny carrying result die

they carry dominant markers so easy to identify

balancers cannot homozygoze--progeny die

useful way to preserve genotype for many generations

screen for recessive embryonic mutants

if you cross two fish heterozygotic for a mutation, ~25% of next generation may show mutant phenotype

you need to wait until F2 or F3 generation (depending on what you cross F1 heterozygote with)

dominant mutation can be observed in F1 generation

Dorsal protein required for what fates

how

embryos with no DL become

ventral fates

after fertilization, Dl prots move into nuclei on the ventral side via Toll pathway

embryos with no DL become dorsalized

toll pathway

toll protein

signal

help set up dorsal ventral axis in drosophila emrbyos

gets Dorsal protein into nuclei on ventral side

toll protein: transmembrane protein in plasma membrane surrounding the embryo

signal Spatzle (Spz) emanates from ventral side and activates Toll receptor

1. activation of Toll

2. Pelle phosphorylates Cactus (causes cactus degrad.)

3. Dl freed to enter nuclei

no dorsal protein, no

ventral fates

whole embryo is dorsalized

no cactus protein, no

dorsal fates

whole emrbyo ventralized

epistasis

when used as a genetic tool what can it detect

what do you need in terms of the two genes to tell anything?

masking of one mutant phenotype by another mutant phenotype

literaly means "stand upon"

powerful genetic tool to detect gene interaction

can order genes in a pathway

you need TWO DIFFERENT PHENOTYPES

SNP

single nucleotide polymorphism

can be used as molecular marker (site of heterozygosity) in mapping mutations

RFLP

restriction fragment length polymorphism

can be used as molecular marker for mapping mutations

molecular marker

used for what

site of heterozygosity

how they map disease locus

meiotic recombination via crossing over

can be used as tool to tell you what

place loci on genetic map

FLP

what is it

when is it useful

yeast flippase recombinase

increases frequency at which mitotic recombination occurs (at flipase recombination target sequences)

can be used to induce loss of heterozygosity

trace mutations

FRT

flipase recombination target sequences

from yeast

you can insert into drosophila along with FLP to induce mitotic recombination at higher frequency

to create clones of cells that are homozygous for a mutation

when can mitotic recombination be useful when studying an organism

why would you want to induce it in experiments?

can be used to induce clone of cells that are homozygous for a mutation

useful when dealing with traits necessary for development in an organism thus preventing use of homozygous organism

crossing over in mitosis can be mediated by

FLP

yeast flippase recombinase

FLP / FRT system

how does it work

where do you insert FRT

by expressing an FRT region nearer to the centromere than the gene of interest, chromosomes can cross over at this point so that each chromosome pair will have one mutant and one wild type chromatid instead of identical ones as in normal case

one possible segregation pattern will result in daughter cells that exhibit loss of heterozygosity

nondisjunction can also happen in mitosis

how can it be useful

can use it to induce loss of heterozygosity

standard methodology for indentifying genes that contribute to a partic biological property

four steps and what kind of tests to you use at ea.

1. screen for mutants collect large set of muts

2. how many gene loci are involved and which mutations are alleles of same gene (complementation test)

3. what is gene interaction (double mutant tests)

4. determine molecular nature of your genes--what do they encode

screen for recessive embryonic mutants

sperm gets mutagenized in one parent--other parent is homozygous wild type

F1 is heterozygous

cross F1 with homozygous wild type

F2 are all wild type phenotype

cross them with each other

you should see some mutant phenotype in F3

(25% of crosses btw two heterozygote crosses)

complementation test

what does it tell you

mutant alleles need to be what

what is complementation?

cross mutants pairwise

how many genes are involved

and

which alleles belong to each gene

mutant alleles need RECESSIVE

complementation = production of wild-type phenotype when two recessive mutant alleles are brought together

gene interaction assays powerful tool to

order genes in what type of pathways

regulatory

or

substrate based

Epistatic gene lies upstream or downstream in

regulatory pathway

substrate pathway

regulatory: downstream

substrate based: upstream

three types of gene interaction

epistasis

supression

enhancement

difference btw enhancement and suppression?

in supression revert to wt

in enhancement --different phenotypes

supression screens

screens to find interacting genes

make double mutants and looks for progeny that are closer to the wild type phenotype

synthetic lethals

what is it and what does it tell you

when two viable single mutants are double crossed, the resulting double mutants are killed

indication that two genes / gene products interact

mis-segregation is

non disjuction during meiosis or mitosis

gene interaction assays powerful tool to do what

order genes in regulatory and substrate-based pathways

1. if products of meiosis show 4 combinations in equal quarters, what has occurred

2. if products of meiosis show 50% 50% breakdown, what has occurred

3. if numbers don't break up easiliy--roughly 50% then 25% 25%

1. independent assortment btw unlinked genes

2. meiosis of linked genes

3. crossing over btw linked genes has lead to recombination