Population Genetics
CHAPTER 5.0 : POPULATION GENETICS
PART A : MULTIPLE CHOICE QUESTIONS
1. Albinism in man is controlled by a recessive allele a. In a population, the frequency of albinism
is one for every 40 000 individuals. What is the frequency of allele a?
A. 0.05% C. 5%
B. 0.5% D. 50%
2. The ability to taste PTC is controlled by the dominant allele T, while the inability to taste PTC is
controlled by the recessive allele t, in a population, 70% can taste PTC. By assuming the
population is in equilibrium, what is the frequency of allele t in the population mentioned?
A. 0.20 C. 0.45
B. 0.30 D. 0.55
3. The genotype frequency of a mutant which is recessive homozygous is 0.16. What is the
frequency of the mutant allele?
A. 0.84 C. 0.40
B. 0.60 D. 0.32
4. The frequency of the allele B in a population at genetic equilibrium is 0.7. What is the frequency
of the Bb genotype?
A. 0.21 C. 0.49
B. 0.42 D. 0.70
5. The cystic fibrosis ailment on the pancreas is a condition of recessive homozygous. If one in
every 2000 individuals in a population suffers this ailment, what is the frequency of the gene in
that population?
A. 0.001 C. 0.043
B. 0.022 D. 0.977
6. Genes reservoir for a population would reach the equilibrium level if …
A. the size of the population is small.
B. natural selection occurs.
C. reproductions happen selectively.
D. mutation does not occur in the population.
7. In a population of humans in Africa, 1.0% of its individuals suffer from the sickle-cell anaemia.
What is the percentage of the individuals in the population that possess abnormal haemoglobin
which is heterozygous?
A. 1% C. 18%
B. 10% D. 90%
8. In a type of mammal, genes for the albino are recessive to the brown hair genes. In the
investigation, it is found that 72 out of 500 mammals are albinos. What is the gene frequency
for the heterozygous albinos in that population?
A. 0.75 C. 0.38
B. 0.47 D. 0.25
9. Consider a hypothetical population in equilibrium with a gene having alleles A and a. This
population consists of 500 individuals such that 125 individuals are genotype AA, 250 are Aa
and 125 are genotype aa. Therefore, the allele frequency for allele A is …
A. 1.00 C. 0.50
B. 0.75 D. 0.25
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Population Genetics
10. If undisturbed by other forces, random sexual reproduction among members of a large
population in nature leads to …
A. new species.
B. changes in gene frequencies.
C. generations of unchanged gene frequencies.
D. a change in the frequency of 2pq, but not p2 or q2.
PART B : STRUCTURED QUESTIONS
1. Phenylketonuria (PKU) is a genetic diseases controlled by the recessive allele. It is also an
inborn error of phenylalanine metabolism and leads to severe mental retardation.
Table 1 shows the number of the normal and the abnormal individuals in a population.
YEAR 1995 2005
The number of the normal individuals 4996 4992
The number of the abnormal individuals (having (PKU) 4 8
Total 5000 5000
Table 1
a) Calculate the frequency of the recessive allele in 1995 and 2005.
[6 marks]
b) Give the conclusion of the allele frequency at (a) (i).
___________________________________________________________________
[1 mark]
c) Give three assumptions to calculate the allele frequency.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
[3 marks]
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Population Genetics
2. a) (i) State the Hardy-Weinberg principle.
___________________________________________________________________
___________________________________________________________________
[2 marks]
(ii) List three conditions for this principle to be achieved.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
[3 marks]
b) In a randomly breeding population of mice, black coat (H) is dominant to white coat (h). In
the population, 36% have white coats.
Calculate the genotypic frequency of black coated mice in this population.
[2 marks]
c) In a human population, the frequency of the recessive individuals for extra-long eyelashes is
90 per 1000. What is the individual percentage of this population that carries recessive allele
but displays the phenotype of short eyelashes?
[3 marks]
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Population Genetics
3. A species of insects may exist as a dark variety or a fair variety. The dark trait is dominant. In a
population of 5000 insects, there are 950 dark insects. By using the Hardy-Weinberg
equation (p2 + 2pq + q2 = 1), calculate
i. The frequency of the ‘fair’ allele. [3 marks]
ii. The frequency of the ‘dark’ allele. [2 marks]
iii. The number of heterozygous insects in the population. [3 marks]
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Population Genetics
Part C: Essay Questions
1. The allele for black hair (B) is dominant over that for grey hair (b). The alleles for B and b have
frequencies p and q respectively. In a randomly mating population of 600 hamsters, 216 have
grey hair.
a) What is meant by a randomly mating population?
[1 mark]
b) Assuming that the Hardy-Weinberg principle applied,
(i) calculate the frequency of the dominant allele and recessive allele in the population.
[2 marks]
c) If all the 216 hamsters with grey hair were killed and the rest were allowed to mate randomly,
(i) calculate the frequency of the dominant and recessive alleles in the new
generation.
[7 marks]
(ii) calculate the various genotypes of the F1 offspring and their frequencies.
[3 marks]
(iii) calculate the percentage of the hamsters with black hair and grey hair in the F1
population.
[2 marks]
2. In large population of butterflies, 557 are white while 396 are brown. Assume that white color is
dominant, determine the followings.
(i) Allelic frequencies of each allele
[6 marks]
(ii) Expected genotypic frequencies
[3 marks]
(iii) Number of heterozygous butterflies
[2 marks]
(iv) Expected phenotypic frequencies
[2 marks]
(v) Assuming that Hardy-Weinberg equilibrium is met, how many white butterflies would you
expect to find among the 1234 butterflies of the next generation?
[2 marks]
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