Term
· Who was Gregor Mendel & why is he associated with the study of heredity?
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Definition
Johann Gregor Mendel, universally known as the "Father of Genetics,"
Gregor Mendel returned to St. Thomas to teach physics. It was there that Gregor Mendel was inspired to study genetic variation and hybridization by combining and breeding different kinds of pea plants. His experiments led to discoveries which are now called "Mendel's Laws of Inheritance."
In his research, Gregor Mendel discovered that offspring inherit two genes, one from the mother and one from the father. If these two genes are different, then the offspring takes on the dominant gene, and the recessive gene produces no visible result. Gregor Mendel estimated that this process, later known as "Mendel's Law of Segregation," could be applied to all species, including humans.
Mendel's passion for science and mathematics led to the combination of different sciences to study biological quandaries. Gregor Mendel is also well known for first applying the methods of statistical investigation to biological sciences. In 1866, when he published his work inProceedings of the Natural History Society of Brunn it was met with skepticism. Scientists didn't believe that Mendel's research had much relevance outside of the plant kingdom, and so it was largely ignored and seldom cited.
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Term
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Definition
an array of the chromosomes found in an individual's cells at metaphase of mitosis and arranged in homologous pairs and in order of diminishing size
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A way to test for chromosomal mutations
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Term
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Definition
A gene is the basic physical and functional unit of heredity. Genes, which are made up of DNA, act as instructions to make molecules called proteins. In humans, genes vary in size from a few hundred DNA bases to more than 2 million bases. The Human Genome Project has estimated that humans have between 20,000 and 25,000 genes.
Every person has two copies of each gene, one inherited from each parent. Most genes are the same in all people, but a small number of genes (less than 1 percent of the total) are slightly different between people. Alleles are forms of the same gene with small differences in their sequence of DNA bases. These small differences contribute to each person’s unique physical features.
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Term
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Definition
| A genome is an organism’s complete set of DNA, including all of its genes. Each genome contains all of the information needed to build and maintain that organism. In humans, a copy of the entire genome—more than 3 billion DNA base pairs—is contained in all cells that have a nucleus. |
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Term
· How many chromosomes do humans have? How many pairs? What is the difference between a sex chromosome & an autosome?
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Definition
In humans, each cell normally contains 23 pairs of chromosomes, for a total of 46. Twenty-two of these pairs, called autosomes, look the same in both males and females. The 23rd pair, the sex chromosomes, differ between males and females. Females have two copies of the X chromosome, while males have one X and oneY chromosome.
So: 46 chromosomes. 23 pairs.
Difference: An autosome is any of the 23 chromosomes which is not an X or Y chromosome. A sex chromosome is effectively the same as an autosome, apart from depending upon whether you inherit a Y chromosome or not, a sex chromosome will determine your gender. Hence the name. |
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Term
· What is an allele?
o What does it mean if alleles are homozygous? Heterozygous? Dominant? Recessive?
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Definition
-is an alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome.
-one of two or more contrasting characteristics transmitted by alternative forms of a gene. also called allelomorph.
-one of two or more alternative forms of a gene that occupy corresponding loci on homologous chromosomes. each allele encodes a phenotypic feature or a certain inherited characteristic. an individual normally has two alleles for each gene, one contributed by the mother and one by the father. if both alleles are the same, the individual is homozygous, if the alleles are different, the individual is heterozygous. in heterozygous individuals, one of the alleles is usually dominant, and the other is recessive. in humans, for example, the allele for brown eyes is dominant, and the allele for blue eyes is recessive |
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Term
| What is dominant and recessive allele? |
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Definition
A dominant allele is one which expresses what it codes for such as eye color no matter what the other allele is. A recessive allele will only express what it codes for if there is a recessive pair. All alleles come in pairs except on the XY chromosomes. For eye color Brown is dominant and blue is recessive so...
(B=brown b=blue)
BB = brown eyes
Bb = still brown eyes even though there is one blue allele
bb = this is the only combination where you can get blue eyes.
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Term
| Contrast genotype & phenotype |
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Definition
An organism's genotype is its genetic identity. The genotype is comprised of all the genetic material inherited from both parents. The genotype is what "tells" each individual cell how to function. The phenotype is the physical expression of an organism's genotype. For example, if a person's genotype for eye color is one dominant allele for brown and one recessive for blue, then the individual's phenotype would be their actual eye color which in this case would be brown.
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Term
Contrast chromosome & chromatid
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Definition
Chromosome = one length of DNA which contains genes. It would look like this I
Chromosome pair = Within normal cells we have two copies of every chromosome, one from mum and one from dad. The genes on the pair (homologous pair) are the same but can be in different forms e.g one can have the allele for blue eyes and the other for brown. They would look like this I I
Chromatid = Just before cells divide, the DNA replicates itself. The duplicate chromatid is still stuck to the original by the centromere. Each chromosome would look like this X which conists of the original chromosome (now called a chromatid) and the copy chromatid. When chromatids separate and are on their own, they are called a chromosome again.
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Definition
| The study of the mechanism of heredity |
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Term
· Be able to describe (in detail) 3 sexual sources of genetic variation.
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Definition
1. Independent Assortment
•During gametogenesis, maternal & paternal chromosomes are randomly distributed to daughter cells
•Alleles on different pairs of homologous chromosomes are distributed independently
•# of possible gametes = 2n, n = # of homologous pairs
•In humans, 2n = 2223 = 8.5 million possibilities!
2. Crossover and Genetic Recombination
•Genes on the same chromosome are linked
•Chromosomes can cross over, forming a chiasma, & exchange segments
•Resulting chromosomes have mixed contributions from each parent
3. Random Fertilization
•1 egg is fertilized by 1 sperm in a random manner
•Because of independent assortment and random fertilization, an offspring represents 1 out of 72 trillion (8.5 million ´ 8.5 million) zygote possibilities!
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Term
· Be able to describe the following 4 types of inheritance & give an example: dominant-recessive, incomplete, multiple allele, polygenic.
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Definition
1. dominant-recessive
•Dominant disorders are uncommon - many are lethal & result in death before reproductive age
•Most genetic disorders are inherited as simple recessive traits
•Ex. Albinism, cystic fibrosis, Tay-Sachs disease
•Heterozygotes are carriers who do not express the trait but can pass it on to their offspring
2. Incomplete Dominance
heterozygous individuals have two different alleles for a certain trait.
ex. •Hypercholesterolemia is a human trait that is incompletely dominant.
3. multiple-allele inheritance
•Some genes exhibit more than 2 allele forms (ex. ABO blood typing)
•3 alleles (IA, IB, i) determine ABO blood type in humans
•IA & IB are codominant (both are expressed if present), & i is recessive (O type blood.
4. Sex-linked inheritance
•Inherited traits determined by genes on sex chromosomes
•X chromosome has >2500 genes
•Y chromosomes carry about 78 genes
•X-linked genes are found only on X chromosome
ex. hemophilia, red-green colorblindness, duchenne muscular dystrophy
5. Polygene inheritance
Polygenic inheritance is when a single trait is controlled by 2 or more sets of alleles. Most human traits are polygenically inherited. Examples would be skin and eye color. This explains how you can have several different phenotypes for one trait and how parents can have offspring with eye color or skin color different from what they have.
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Term
| 2Benefits of genetic screening/counseling/therapy and 2 downfalls. |
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Definition
Genetic testing has potential benefits whether the results are positive or negative for a gene mutation. Test results can provide a sense of relief from uncertainty and help people make informed decisions about managing their health care. For example, a negative result can eliminate the need for unnecessary checkups and screening tests in some cases. A positive result can direct a person toward available prevention, monitoring, and treatment options. Some test results can also help people make decisions about having children. Newborn screening can identify genetic disorders early in life so treatment can be started as early as possible.
Downfall: Although gene testing poses little physical risk--usually no more than giving a blood sample--it can seriously affect a person's life.
A test confirming the risk of a serious disease can trigger profound psychological consequences.
Genetic counseling: Genetic counselors have a vital role to play.
These specially trained health professionals are skilled at supporting individuals when testing is being considered, when test results are received, and during the weeks and months afterward.
Gene therapy: The basis of gene therapy is find a gene that is not functioning right and to insert a healthy portion into that gene. To find these genes, scientists must perform genetic tests or genetic screening to see i f the gene that causes for example, cystic fibrosis, is present. This genetic testing is producing much controversy and raising many ethical and legal problems. Many believe that this is an invasion of privacy. They believe that if prenatal tests are performed that these could lead to an increase in the number of abortions. Many people that hear a positive test for a disease are now are faced with a dilemma. That dilemma is in finding adequate insurance to cover the treatments, which could be gene t herapy, or living out their lives knowing that they carry a gene for a disease
other disadvantages of gene therapy:
- Short-lived nature of gene therapy
- Immune response - Genes injected with a virus may trigger an immune response against the virus.
- Problems with viral vectors (once inside the patient, the viral vector could recover its ability to cause disease).
- Multigene disorders - The genetic material might not get into the right cell, or the right place in the cell’s DNA
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Term
· Compare & contrast amniocentesis & CVS. Why would each be conducted?
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Definition
Definitions
Amniocentesis tests the amniotic fluid that surrounds the fetus in the uterus, acting as a protective cushion. The fluid contains cells sloughed off from the fetus, as well as chemicals naturally secreted from the fetus.chorionic villus sampling (CVS) tests the finger-like projections of the placenta, the organ that provides the interface between mother and fetus for exchange of oxygen, nutrients and waste products. Because the chorionic villi arise from the fetus, they contain the fetus' genetic material. Both amniocentesis and CVS take samples of fetal cells to determine its genetic code and identify any genetic diseases
conducted to determine if anything is wrong with the baby.
CVS can be performed as early as the 10th to 12th weeks of the pregnancy, while amniocentesis is generally done at around the 15th week of pregnancy, when the two layers of the fetal membrane have fused, according to the Mayo Clinic. In contrast to CVS, amniocentesis can also detect neural tube defects and fetal infections or illnesses. Amniocentesis might also be used much later in pregnancy to reduce the volume of amniotic fluid, or to determine if the baby's lungs have matured enough for birth.
Both procedures carry the risks of uterine cramping and vaginal bleeding, Rh sensitization if the mother is Rh negative, and infection. Amniocentesis additionally has risks of leaking amniotic fluid, or injury to the fetus from the needle. The greatest danger for both procedures lies in the risk of miscarriage. According to the Mayo Clinic, for amniocentesis the risk is 1 in 300 to 1 in 500, while for CVS the risk is about 1 in 100
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Term
| What is the purpose of a punnet square? |
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Definition
The purpose of a punnet square is to help you see all the different possible genotypes of a particular trait.
___p _ p
P PP Pp
p pp pp
For example. Here you have the two parents, with trait P. We'll say this determines the number of arms the offspring has. (Yes, this is unrealistic, but let's just go with it.) If a dominant gene is inherited (P), then the offspring will have 4. In no dominant gene is inherited, the offspring will have 6.
By making a chart, with the father's genotype on one axis and the mother's on the other, and mapping the different possible combinations, you can see what thechances are of each Phenotype, or genotype, depending on what you're looking for.
In this example, there is a 50% chance that the child will have 4 arms. |
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