QUESTION 83 (6 marks)
A biologist genotypes every adult in a small diploid frog population. There are 25 AA, 50 Aa and 25 aa frogs in year 1. In year 2 there are 40 AA, 40 Aa and 20 aa frogs.
a) Calculate the frequency of allele A in each year. [3 marks]
b) Determine the change in A frequency and identify whether this is microevolutionary change. [2 marks]
c) Explain why genotype counts alone do not identify the process responsible for the change. [1 marks]
Practice marking scheme
Answer
a) 0.50 and 0.60. b) +0.10; it is microevolution. c) Several processes can change allele frequencies.
Working
Year 1 has A alleles out of 200; year 2 has out of 200. Thus frequency rises from 0.50 to 0.60, an increase of 0.10 or ten percentage points. A change in a population’s allele frequency is microevolution. Selection, drift, migration or other processes could contribute; these counts alone do not isolate a cause.
Marking criteria
- Counts total alleles as 200 per year. [1 mark]
- Calculates initial A frequency as 0.50. [1 mark]
- Calculates later A frequency as 0.60. [1 mark]
- Calculates a change of +0.10. [1 mark]
- Identifies allele-frequency change as microevolution. [1 mark]
- Recognises that the data alone cannot distinguish its possible causes. [1 mark]
Practice question aligned to the current QCAA syllabus; review the worked solution and marking criteria.
View the QCAA syllabusCompare your working with the guide above.