# Explain how the founder effect can lead to speciation in a small population that becomes geographically isolated from its parent population.

> IB DP Biology Higher Level (2023 syllabus) — A4.1 Evolution and speciation · Explain · 4 marks

## Mark scheme (4 marks)

1. The founder effect occurs when a small number of individuals establish a new population, carrying only a subset of the genetic variation present in the original population.
2. Allele frequencies in the founder population differ from those in the parent population due to chance sampling (genetic drift), so the two populations begin to diverge genetically.
3. Geographic isolation prevents gene flow between the founder and parent populations, so mutations and selection pressures act independently on each population.
4. Over time, sufficient genetic divergence accumulates so that members of the two populations can no longer interbreed successfully to produce fertile offspring, completing speciation (reproductive isolation is established).

## Key terms

- [founder effect](https://www.gradenine.co.uk/glossary/founder-effect)
- [speciation](https://www.gradenine.co.uk/glossary/speciation)

## 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)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-founder-effect-can-70ac0f5b) · Published by Druglandscape Ltd.