A level Biology B · Edexcel 9BI0 · Topic 8C
Population genetics
Key points
- A gene pool is all the alleles in a population; allele frequency is the proportion of a particular allele.
- Hardy–Weinberg: and , where and are the frequencies of the dominant and recessive alleles.
- Typical exam step: work out from the number of homozygous recessive individuals, take the square root to get , then and carriers = .
- The principle assumes a large population, random mating, no mutation, no migration and no selection.
- Genetic drift: random changes in allele frequency, strongest in small populations.
- Founder effect (a few individuals start a new population) and genetic bottleneck (a population crashes) both reduce genetic diversity.
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Evolution happens in populations, not individuals. Population genetics tracks how common each allele is and explains why those frequencies change from one generation to the next.
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