Question

RANDOM GENETIC DRIFT Suppose that the assumptions of Hardy-Weinberg Equilibrium hold true and that the frequencies of the three possible genotypes are 0.81 (A1A1), 0.18 (A1A2), and 0.01 (A2A2). Individuals with the genotype A1A1 are the progeny of parents that each contributed an A1 allele. Because we are using p to represent the frequency of the A1 allele, if the gametes of parents join randomly, the frequency of A1A1 individuals in the progeny can be represented by p^2. Similarly, q^2 represents the expected frequency of individuals with the A2A2 genotype, and 2pq is the expected frequency of heterozygotes (A1A2). Therefore, we can conclude that in this population p = 0.9 and q = 0.1. This description seems reasonable enough. Up to this point all we have done is associate some mathematical notation with the genotypes that exist in a population. We can use this notation and the relationship that we have established between gametes and progeny, which is just based on Mendelian genetics, to make predictions about allele and genotype frequencies in the future. 1. Suppose that members of the above population make gametes, and release them into the water, as many marine invertebrates do (referred to as broadcast spawning). (a) What would the frequency of genotypes be in the next generation? (b) What would the frequency of genotypes be in subsequent generations? 2. Now, what if the population under consideration consisted only of a relatively small number of individuals, say 50? Considering a finite population introduces a wrinkle. What happens in finite populations that differs from the results we observed above with the model of populations of infinite size? Alternatively, what happens to genotype and allele frequencies if gametes carrying a particular allele (e.g., A1) are less viable than other gametes (i.e., selection acts against individuals carrying A1)?

RANDOM GENETIC DRIFT
Suppose that the assumptions of Hardy-Weinberg Equilibrium hold true and that the frequencies of the three
possible genotypes are 0.81 (A1A1), 0.18 (A1A2), and 0.01 (A2A2). Individuals with the genotype A1A1 are the
progeny of parents that each contributed an A1 allele. Because we are using p to represent the frequency of
the A1 allele, if the gametes of parents join randomly, the frequency of A1A1 individuals in the progeny can be
represented by p^2. Similarly, q^2 represents the expected frequency of individuals with the A2A2 genotype, and
2pq is the expected frequency of heterozygotes (A1A2). Therefore, we can conclude that in this population p =
0.9 and q = 0.1.
This description seems reasonable enough. Up to this point all we have done is associate some mathematical
notation with the genotypes that exist in a population. We can use this notation and the relationship that we
have established between gametes and progeny, which is just based on Mendelian genetics, to make
predictions about allele and genotype frequencies in the future.
1. Suppose that members of the above population make gametes, and release them into the water, as many
marine invertebrates do (referred to as broadcast spawning).
(a) What would the frequency of genotypes be in the next generation?
(b) What would the frequency of genotypes be in subsequent generations?
2. Now, what if the population under consideration consisted only of a relatively small number of individuals,
say 50? Considering a finite population introduces a wrinkle. What happens in finite populations that differs
from the results we observed above with the model of populations of infinite size?
Alternatively, what happens to genotype and allele frequencies if gametes carrying a particular allele (e.g., A1)
are less viable than other gametes (i.e., selection acts against individuals carrying A1)?

Added by Trevor C.

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