# Describe how a genetic bottleneck can reduce the genetic diversity of a population. Include in your answer an explanation of why reduced genetic diversity makes a species more vulnerable to extinction.

> AQA A-Level Biology (7402) — 3.4.4 Genetic Diversity and Adaptation · Describe · 5 marks

> Cheetahs are thought to have experienced a genetic bottleneck thousands of years ago. Today, cheetahs show very little genetic variation compared to most other mammals.

## Mark scheme (5 marks)

1. A genetic bottleneck occurs when the population size is drastically reduced
2. Many alleles are lost from the gene pool
3. The surviving individuals only carry a small range of alleles, so the remaining population has low genetic diversity
4. If the environment changes or a new disease arises, individuals with alleles that provide resistance / adaptation may not exist in the population
5. Natural selection cannot act on variation that does not exist, so the population cannot adapt, increasing the risk of extinction

## Key terms

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

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Source: [GradeNine](https://www.gradenine.co.uk/q/describe-how-a-genetic-bottleneck-can-31929998) · Published by Druglandscape Ltd.