# Explain why selective breeding of crop plants can reduce genetic diversity and suggest why this reduction in genetic diversity could be a disadvantage for the crop population.

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

> Farmers have selectively bred wheat plants for thousands of years to produce high-yielding varieties. Modern wheat crops are grown across large areas and are often genetically very similar to one another.

## Mark scheme (5 marks)

1. Selective breeding involves humans choosing organisms with desired characteristics to breed together
2. Only a small number of alleles / gene variants are passed on to offspring (reducing the gene pool)
3. Over successive generations the population becomes more genetically similar / homozygous
4. If a new disease or pathogen emerges, most/all plants may be susceptible because they lack the alleles for resistance
5. The population cannot adapt to changed environmental conditions because there is insufficient genetic variation for natural selection to act upon

## Key terms

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

## Related

- [Revision notes for AQA A-Level Biology (7402)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain / Suggest" 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-why-selective-breeding-of-crop-3a968a50) · Published by Druglandscape Ltd.