Flashcards in Heredity and genes Deck (17)
What are Mendels Laws
1. segregation: during meiosis, the two different alleles in a chromosome pair separate such that each gamete contains only 1 allele, leading to novel combinations in offspring.
2. independent assortment: if the genes are on different chromosomes, inheriting one gene is independent of the other gene.
3. law of dominance: recessive alleles masked by dominant ones
How did the experiment go, in which Mendel based his first law of segregation?
Monohybrid pea colour experiment
P: AA x aa (truebreeds)
F1: Aa x Aa (all yellow peas)
F2: 3 : 1 yellow :green
Disproves blending of alleles (dilution problem) because no intermediate forms.
How did the experiment go, on which Mendel based his second law of independent assortment? What were his conclusions based on this?
Dihybrid pea colour + shape experiment.
P: AABB x aabb
F1: AaBb x AaBb (all yellow and round)
1) If linked genes: A and B together, a and b always together. Only parental alleles (AB for the father, ab for the mother) can be recombined. Result: 3:1 yellow + round : green + wrinkled
2) If indepenent: A and B, a and b not necessarily together. Result: 9:3:3:1 yellow + round: yellow + wrinkled: green + round: green + wrinkled.
This is what Mendel found, hence the law.
Assumptions Hardy Weinberg
1. random mating
2. no migration
3. no selection
4. large population
5. no mutation
What is an important implication of genetic drift? How can we use it, theory?
Neutral theory of molecular evolution
The neutral genetic drift causes more divergence the longer a species or population has been separated. So you can see how long ago they separated by comparing the DNA.
What are some exceptions to simple Mendelian inheritance?
- polygenic traits
- pleiotropy: 1 gene encodes many traits
- epistasis: one gene changes the phenotypic expression of the other
- co-dominance: both alleles are fully expressed. (blood type, flowers with 2 colors)
incomplete dominance: intermediate form of two alleles (a flower with an intermediate color)
- genes with more than 2 possible alleles/polymorphs
What is coefficient of relatedness (r)
The average genetic material you share with a family member because of inheritance. Probability an allele is identical by descent. A measure of how much more genetically similar you are to the relative compared to the general population.
Central ideas of quantitative genetics and relation to polygenic traits?
Phenotypic variation = genetic variation + environmental impact.
To know how much genetic variation is causing phenotypic variation (heritability), you cannot use simple Mendelian inheritance laws -> quantitative genetics.
Uses the basic insight of the coefficient of relatedness to calculate heritability because closer relatives will be more similar to each other IF the trait is heritable.
How are twin studies used to estimate heritability with the help of the coefficient of relatedness?
twin studies: MZ twins have r=1 and DZ have r= 1/2. Both have shared environment=1 and nonshared environment=0. Phenotypic variation will thus be due to r=1/2.
Falconer heritability = difference phenotype/difference genotype. = difference phenotype / 0.5. Because in this case the difference in genotype is 0.5.
What are ACE models?
More sophisticated models than Falconer heritability estimates, to estimate the influence of A (genotype), C(shared environment) and E(nonshared environment). Used in quantitative genetics.
Many ACE models show that A > 0 for basically anything ever studied, and E is often more important than C.
What are adoption studies used for and how do they work?
Also to estimate in polygenic traits how much is heritability and how much is environment. If a child is adopted, comparison between biological and social parent shows which one is more similar. Gives insight into relative strengths A (genes) and C (shared environment)
Does Arriva suck?
Does natural selection happen quicker with high or low heritability?
Law of independent assortment: when does it apply and when not? Explain why.
Applies when genes are on a different chromosome and when genes are far apart on the same chromosome due to recombination. Doesn't apply when genes are close on a chromosome: linked.
If they are linked, crossing over (recombination) during meiosis is very unlikely to happen just between the loci.
How do association studies work?
In unrelated people, looks 'in the neighbourhood' of genes associated with a phenotypic trait. Because of recombination, the genes will be mixed a lot in the general population. So if you look for suspicious polymorphisms (specifically, SNPs) in your affected participant group and find they all have it, it could be that gene causing the trait, but also the genes lying close to it. It is merely 'associated with' the trait.
How do linkage studies work?
In families, where some members have the trait of interest and some have not, the genotype of each person is examined for genes whose location is known. These are called markers. If all the family members who have the trait share the same marker alleles on a certain location on a specific allele, there is strong evidence that the gene for the trait is somewhere close.