# A population of rabbits lives in a field. Over several years, a new strain of a pathogen spreads through the rabbit population. Some rabbits survive the infection whilst others die. Explain how natural selection could lead to most rabbits in the field eventually being resistant to this pathogen.

> OCR A-Level Biology B — Advancing Biology (H422) — 4.4 Populations and evolution · Explain · 5 marks

> Rabbits in a field are affected by a pathogen. Within the population there is variation in resistance to this pathogen. Some rabbits survive infection; others do not.

## Mark scheme (5 marks)

1. There is variation in resistance to the pathogen within the rabbit population
2. Rabbits with greater resistance to the pathogen are more likely to survive
3. Surviving rabbits are more likely to reproduce and pass on the alleles/genes for resistance to offspring
4. Non-resistant rabbits are less likely to survive and reproduce, so resistance alleles/genes become more common in the population over generations
5. Over many generations, most of the rabbit population carries the resistance, so the majority of rabbits are resistant to the pathogen

## Key terms

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

## Related

- [Revision notes for OCR A-Level Biology B — Advancing Biology (H422)](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/a-population-of-rabbits-lives-in-1f51520b) · Published by Druglandscape Ltd.