# Explain how the accumulation of mutations over time can contribute to speciation.

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

> Mutations arise spontaneously in populations at a low but constant rate. Over many generations, different populations may accumulate distinct sets of mutations.

## Mark scheme (4 marks)

1. Mutations introduce new alleles / new genetic variation into a population.
2. Natural selection acts on this variation, favouring alleles that increase fitness in the local environment, so different populations accumulate different allele frequencies.
3. Over time, the two populations diverge genetically / become genetically distinct from one another.
4. Eventually reproductive isolation arises / individuals from the two populations can no longer interbreed to produce fertile offspring, so they are considered separate species.

## Key terms

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

## Related

- [Revision notes for IB DP Biology Standard 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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-accumulation-of-mutations-9a9719c7) · Published by Druglandscape Ltd.