A population of an island lizard species has been monitored over several discrete generations. A single genetic locus with three possible alleles is relevant: a1 (ancestral), a2 (a new variant that arose after generation 0), and a3 (not present initially). The population is diploid.
Timeline and observed allele frequencies (proportion of all alleles at the locus) are shown below. The population size is approximately 10,000 adults and stable from generation 0 to generation 4. No migration is recorded during generations 0–4. At the end of generation 4 a hunting event reduces the island population to 30 surviving adults (a severe bottleneck). Immediately after this bottleneck, 5 adult lizards arrive from the mainland and join the survivors; all 5 migrants are homozygous for allele a3. After migration the population size recovers to 200 by the next census (generation 6) but remains isolated from other populations thereafter.
| Generation | Frequency of a1 | Frequency of a2 | Frequency of a3 |
|---|---|---|---|
| 0 | 1.000 | 0.000 | 0.000 |
| 1 | 0.995 | 0.005 | 0.000 |
| 2 | 0.988 | 0.012 | 0.000 |
| 3 | 0.982 | 0.018 | 0.000 |
| 4 | 0.980 | 0.020 | 0.000 |
The monitoring programme estimates that, prior to generation 1, spontaneous mutation at this locus in similar reptiles is typically very rare (on the order of 10^-6 to 10^-8 per allele per generation). No direct fitness measurements for a2 are available from the field.
After generation 4, the population is reduced to 30 survivors and then 5 migrants (all homozygous for a3) join immediately. Calculate the expected frequency of allele a3 immediately after the migrants join (treat the population as adults present after arrival). Then evaluate the relative short-term and longer-term effects of genetic drift, gene flow and mutation on the island population’s gene pool from generation 4 onwards. In your evaluation, state which process or processes are likely to be most influential at each stage and justify your reasoning with reference to population size and the numbers given.
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Create Free Account Log inThis is a free HSC HSC Biology practice question worth 4 marks, testing your understanding of Evaluate gene pool change processes. It falls under Mutation in Module 2: Genetic Change. Submit your answer above to receive instant AI-powered marking and personalised feedback.
Students learn about natural and human-induced causes and effects of genetic change, including mutations, environmental pressure and uses of biotechnology. Students investigate how the processes of inheritance and evolution are applied. The work of scientists in various fields of work, including agriculture, industry and medicine, can be explored within the context of biotechnology. The impact of biotechnology on biological diversity is also explored in this module.
Inquiry question: How does mutation introduce new alleles into a population?
evaluate the effect of mutation, gene flow and genetic drift on the gene pool of populations
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