Evolution__3rd_Edition

136 PART 2 / Evolutionary Genetics
Study and review questions
1 The following table gives genotype frequencies for five
populations. Which are in Hardy–Weinberg equilibrium?
For those that are not, suggest some hypotheses for why
they are not.
Genotype
Population AA Aa aa
1 25 50 25
2 10 80 10
3 40 20 40
4 0 150 100
5 2 16 32
2 For genotypes with the following fitnesses and
frequencies at birth:
Genotype AA Aa aa
Birth frequency p 2 2pq q 2
Fitness 1 1 1 − s
(a) What is the frequency of AA individuals in the adult
population? (b) What is the frequency of the gene A in
the adult population? (c) What is the mean fitness of the
population?
3 What is the mean fitness of this population?
Genotype AA Aa aa
Birth frequency 1
/3
1
/3
1
/3
Fitness 1 1 − s 1
4 Consider a locus with two alleles, A and a. A is
dominant and selection is working against the recessive
homozygote. The frequency of A in two successive
generations is 0.4875 and 0.5. What is the selection
coefficient (s) against aa? (If you prefer to do it in your
head rather than with a calculater, round the frequency
of a in the first generation to 0.5 rather than 0.5125.)
5 What main assumption(s) is (or are) made in
estimating fitnesses by the mark–recapture method?
6 Here are some adult genotype frequencies for a
locus with two alleles. The polymorphism is known
to be maintained by heterozygous advantage, and the
fitneses of the genotypes are known to differ only in
survival (and not infertility). What are the fitnesses (or
selection coefficients) of the two homozygotes, relative
to a fitness of 1 for the heterozygote?
Genotype AA Aa aa
Frequency among adults 1
/6
2
/3
1
/6
7 There are two populations of a species, called
population 1 and population 2. Migrants move from
population 1 to 2, but not vice versa. For a locus with
two alleles A and a, in generation n, the gene frequency
of A is 0.5 in population 1 and 0.75 in population 2; in
generation 2 it is 0.5 in population 1 and 0.625 in
population 2. (a) What is the rate of migration, measured
as the chance an individual in population 2 is a firstgeneration
immigrant from population 1? (b) If the rate
of migration is the same in the next generation, what will
the frequency of A be in population 2 in generation 3?
[Questions 8–10 are more in the nature of questions for
further thought. They are not about things explicitly
covered in the chapter, but are slight extensions.]
8 What is the general effect of assortative mating on
genotype frequencies, relative to the Hardy–Weinberg
equilibrium, for (a) a locus with two alleles, one
dominant to the other; and (b) a locus with two alleles,
and no dominance (the heterozygote is a distinct
phenotype intermediate between the two
homozygotes)? And (c) what is the effect on genotype
frequencies of a mating preference, in which females
preferentially mate with males of (i) the dominant, and
(ii) the recessive phenotype?
9 Derive a recurrence relation, giving the frequency of
the dominant gene A one generation on (p′) in terms of
the frequency in any generation (p) and of the selection
coefficient (s) for selection against the dominant allele.
10 Derive the expression for the equilibrium gene
frequency (p*) for the mutation–selection balance
when the disadvantageous mutation is recessive.
..