Download Practice Problems: Population Genetics

Practice Problems: Population Genetics
1. The gamma globulin of human blood serum exists in two forms, Gm(a+) and
Gm(a-), spedified respectively by an autosomal dominant gene Gm(a+) and
its recessive allele Gm(a-). Broman et al. (1963) recorded the tabulated
phenotypic frequencies in three Swedish populations. Assuming the
populations were at Hardy-Weinberg equilibrium, calculate the frequency of
heterozygotes in each population.
Region
No. Tested
Phenotype %
Norbotten County
Stockholm city and
rural district
Malmohus and
Kristianstad counties
139
509
Gm(a+)
55.40
57.76
Gm(a-)
44.60
42.24
293
54.95
45.05
2. A sheep rancher in Iceland finds that the recessive allele y for yellow fat has
become established in his flock of 1,024 and that about 1 out of every 256
sheep expresses the trait.
a) The rancher wishes to know how many of the normal sheep carry the
recessive allele. Assuming the population is randomly mating for this
gene and all genotypes have the same reproductive fitness, what is this
proportion?
b) How many of the 1,020 white animals can be expected to be
homozygous?
3. Among 2,820 Shorthorn cattle, 260 are white, 1,430 are red, and 1,130 are
roan. Is this consistent with the assumption that the traits are controlled by
a single pair of autosomal alleles and that mating has been at random for this
allele pair?
4. On the basis of allele-frequency analysis of data from a randomly mating
population Snyder (1934) concluded that the ability vs. inability to taste
phenylthiocarbamide (PtC) is determined by a single pair of autosomal
alleles, of which T for taster is dominant to T for nontaster. Of the 3,643
individuals tested in this population, 70% were tasters and 30% were
nontasters. Assume the population satisfies the conditions of HardyWeinberg equilibrium.
a) Calculate the frequencies of the alleles T and T and the frequencies of the
genotypes TT, TT and TT
b) Determine the probability of a nontaster child from a taster x taster
mating.
5. The MN blood-group frequencies (in percent) in a certain population are MM
= 28.38, MN = 49.57, NN = 22.05.
a) Calculate the frequencies of the M and N alleles and determine whether
or not this population is in Hardy-Weinberg equilibrium.
6. A certain large human population is at equilibrium for the autosomal
recessive lethal allele a, which causes death before reproductive age. The
mutation rate A a is 1 in 490,000.
a) What is the equilibrium frequency of a in this population?
b) What is the frequency of heterozygotes?
c) What proportion of individuals would be expected to express this lethal
phenotype?
7. In a human population the equilibrium frequency of congenital total color
blindness, which is caused by a recessive autosomal allele, is 1 in 80,000.
Afflicted individuals have extremely poor vision and may as a result have a
lowered reproductive fitness. If their reproductive fitness is 0.5, what is the
mutation rate necessary to maintain this frequency of the trait in the
population?
8. You wish by artificial selection to reduce the frequency of a recessive trait in
a large randomly mating population in which the frequency of the recessive
allele is 0.5.
a) Show the initial types and proportions of the different phenotypes in this
population, assuming Hardy-Weinberg equilibrium.
b) Determine the frequency of the alleles in the population after one, two,
and three generations of complete selection against the recessive allele
(s=1).
9.
A yak population is in Hardy-Weinberg equilibrium with allele frequencies
p(A) = 0.5 and q(a) = 0.5 for a gene governing color differences. If a new type
of predator appears in the area, calculate the new values of q if:
a) sa/a = 1.0
b) sa/a = 0.70
c) sa/a = 0.10
10. In Drosophila melanogaster, Cncn (red vs. cinnabar eyes), Bb( gray vs. black
body, (and Byby (normal vs. blistery wing) are autosomal pairs of alleles.
Samples of three large natural adult populations, each classified for a
different pair of traits, are found to have the following genotypes:
Population A
Population B
Population C
31 cncn
182 BB
100 ByBy
171 Cncn
391 Bb
372 Byby
60 CnCn
152 bb
40 byby.
Total 262
Total 725
Total 512
Compare these distributions with those expected for a population at HardyWeinberg equilibrium. Propose a reasonable explanation to account for any
differences.
11. If the frequency of an allele d is 0.25 in a migrant population and 0.5 in The
recipient population, and if the migration rate is 0.1, what is the frequency of
d in the recipient population after one generation of migration?