QUESTION 146 (5 marks)
Eight small and eight large isolated populations begin with f(A) = 0.50 at a neutral locus. After ten generations their frequencies are shown. No mutation or migration occurs, and A and a do not affect survival or reproduction.
| Replicate | Small population | Large population |
|---|---|---|
| 1 | 0.1 | 0.46 |
| 2 | 0.2 | 0.48 |
| 3 | 0.35 | 0.49 |
| 4 | 0.45 | 0.5 |
| 5 | 0.55 | 0.5 |
| 6 | 0.65 | 0.51 |
| 7 | 0.8 | 0.52 |
| 8 | 0.9 | 0.54 |
a) Calculate the frequency range in each group and compare the variability. [2 marks]
b) Explain the evolutionary process that best accounts for the difference between groups. [2 marks]
c) Explain why the table does not support selection consistently favouring A. [1 mark]
Practice marking scheme
Answer
Small-population range is 0.80; large-population range is 0.08. The wider chance variation in small populations supports stronger genetic drift, without one shared direction of change.
Working
Small frequencies range from 0.10 to 0.90; large frequencies from 0.46 to 0.54. Random allele transmission can have a much larger proportional effect when fewer individuals contribute. Some small populations increase A and others decrease it; the model explicitly excludes an allele fitness difference, so a common directional selection explanation is unsupported.
Marking criteria
- Calculates small range 0.80. [1 mark]
- Calculates large range 0.08 and identifies greater small-population variability. [1 mark]
- Identifies genetic drift/chance allele sampling. [1 mark]
- Links larger proportional chance effects to smaller population size. [1 mark]
- Uses neutrality and/or the opposite directions of frequency change to reject a uniform advantage. [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.