Allele frequency, speciation and conservationEdexcel International A Level Biology: Subtopic test

1. 1
   In a large population of beetles, body colour is controlled by one gene with two alleles: a dominant allele G for green and a recessive allele g for brown. 16% of the beetles are brown. Assume that the population is in Hardy-Weinberg equilibrium.

   (a)

   What is the frequency of the allele g in the beetle population?

   [1 mark]

   • A0.4
   • B0.16
   • C0.84
   • D0.6

   (b)

   What proportion of the beetles is heterozygous?

   [1 mark]

   • A0.24
   • B0.36
   • C0.48
   • D0.60

   (c)

   State two conditions that must be met for the frequency of the alleles in the beetle population to stay the same from one generation to the next.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Ground squirrels live on both sides of a deep canyon that was cut by a river over thousands of years. The squirrels cannot cross the canyon. The north side of the canyon has wet forest and the south side has dry scrub. Today the squirrels on the two sides differ in coat colour and in the frequencies of many alleles.

   (a)

   Which term describes the formation of new species from populations that are separated by a geographical barrier?

   [1 mark]

   • ASympatric speciation
   • BAllopatric speciation
   • CDirectional selection
   • DGenetic bottleneck

   (b)

   Which observation would give the best evidence that the squirrels on the two sides of the canyon are now separate species?

   [1 mark]

   • AThey live in different habitats
   • BThey differ in coat colour
   • CThey have different allele frequencies
   • DThey cannot breed together to produce fertile offspring

   (c)

   Explain how the canyon could have led to the formation of two species of ground squirrel.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Warfarin is a poison that is used to kill rats. Before warfarin was first used in a farming region, an allele R that gives resistance to warfarin was very rare, with a frequency of 0.001 in the rat population. After 15 years of continuous use of warfarin, the frequency of allele R in the rat population was 0.6.

   (a)

   Explain how the frequency of allele R increased in the rat population.

   [3 marks]

   (b)

   Rats with allele R need much more vitamin K in their diet than rats without it. Use of warfarin in the region is stopped. Predict what will happen to the frequency of allele R over the following decades. Explain your answer.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   On a mountain island, a rare frog that is found nowhere else has fallen to about 80 individuals in the wild because of the spread of a fungal disease and the loss of its forest habitat. A zoo plans a captive-breeding programme for the frog. The island's botanic garden plans to store seeds of a threatened endemic tree, which is being logged, in a seed bank.

   (a)

   Evaluate the use of a zoo captive-breeding programme to conserve the frog.

   [6 marks]

   (b)

   Evaluate the use of a seed bank to conserve the endemic tree.

   [6 marks]

   Total for question 4: 12 marks

End of questions