The Hardy-Weinberg principleAQA A-Level Biology: Subtopic test

1. 1
   A conservation biologist is studying rabbits living on a small island. She records the alleles present in the rabbit population for a gene controlling fur colour and wants to predict the allele frequencies in future generations.

   (a)

   Which term describes all the alleles of all the genes in the island's rabbit population at one time?

   [1 mark]

   • AAllele frequency
   • BGene pool
   • CGenotype frequency
   • DCommunity

   (b)

   In the Hardy-Weinberg equation, p is the frequency of the dominant allele and q is the frequency of the recessive allele. Which expression gives the frequency of the heterozygous genotype?

   [1 mark]

   • A$p^2$
   • B$q^2$
   • C$2pq$
   • D$p + q$

   (c)

   State two conditions that must apply for the biologist's prediction, based on the Hardy-Weinberg principle, to be valid.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Cystic fibrosis is a human genetic disorder caused by a recessive allele, f. The dominant allele, F, is normal. In one population the incidence of cystic fibrosis is 1 in 2500 births. Assume that the Hardy-Weinberg principle applies to this population.

   (a)

   What is the frequency of the dominant allele, F, in this population?

   [1 mark]

   • A0.0004
   • B0.02
   • C0.04
   • D0.98

   (b)

   How many carriers of the cystic fibrosis allele would be expected in a population of 50 000 people?

   [1 mark]

   • A1960
   • B980
   • C20
   • D48 020

   (c)

   Many people with cystic fibrosis die young or do not have children. Explain why the Hardy-Weinberg principle may not predict the frequency of carriers accurately in future generations.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A population of 800 plants of one species has two alleles for flower colour. The allele for red flowers, R, is dominant to the allele for white flowers, r. In the population, 128 of the plants have white flowers. The population is assumed to be in Hardy-Weinberg equilibrium.

   (a)

   Calculate the frequency of the allele R and the number of heterozygous plants in the population. Show your working.

   [3 marks]

   (b)

   Ten years later, 160 of the 800 plants have white flowers. Calculate the new frequency of the allele r, and suggest two reasons why the frequency of r has changed.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A conservation team studies a population of 5000 deer on an island. Coat colour is controlled by one gene with two alleles. The allele for brown coat, B, is dominant to the allele for white coat, b. In the population, 200 of the deer have a white coat. Occasionally, deer from the mainland are brought to the island and breed with the island deer.

   (a)

   Explain what the Hardy-Weinberg principle predicts about allele frequencies, and discuss whether the principle is likely to apply to the island deer.

   [6 marks]

   (b)

   Assuming the Hardy-Weinberg principle applies, calculate the frequency of the allele b and the expected number of deer of each genotype. Predict the number of white deer in the next generation.

   [6 marks]

   Total for question 4: 12 marks

End of questions