# Explain how genetic drift can lead to rapid evolutionary change in small, isolated populations.

> IB DP Biology Higher Level (2023 syllabus) — D4.2 Stability and change · Explain · 4 marks

> A volcanic island is colonised by a small founding group of birds that became separated from a large mainland population. Over several generations, the island population shows markedly different allele frequencies from the mainland population, despite no apparent selection pressure.

## Mark scheme (4 marks)

1. Genetic drift refers to random changes in allele frequencies due to chance events rather than natural selection
2. In small populations, chance sampling errors have a proportionally larger effect, so allele frequencies fluctuate more dramatically between generations
3. Alleles can become fixed (reach 100% frequency) or lost entirely by chance, reducing genetic variation
4. The founder effect is a specific example of genetic drift where the founding population carries only a subset of the original gene pool, so the island population diverges genetically from the mainland population

## Key terms

- [genetic drift](https://www.gradenine.co.uk/glossary/genetic-drift)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-genetic-drift-can-lead-2a8e9e62) · Published by Druglandscape Ltd.