# Explain how natural selection can lead to a change in the frequency of a heritable trait in a population of organisms over several generations.

> IB DP Biology Standard Level (2023 syllabus) — D4.1 Natural selection · Explain · 4 marks

> A population of mice lives in a grassland habitat that becomes progressively drier and paler in colour over many decades. The mice show heritable variation in fur colour, ranging from dark brown to pale sandy.

## Mark scheme (4 marks)

1. Individuals within the population show heritable variation in fur colour (from dark to pale).
2. Pale-furred mice are better camouflaged against the paler habitat and so have a selective advantage, being less likely to be predated.
3. Pale-furred individuals survive longer and reproduce more, passing the alleles for pale fur to a greater proportion of offspring.
4. Over many generations, the frequency of the allele(s) for pale fur increases in the population, so the population becomes predominantly pale-furred.

## Key terms

- [natural selection](https://www.gradenine.co.uk/glossary/natural-selection)

## 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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-natural-selection-can-lead-d5c70d0a) · Published by Druglandscape Ltd.