# In guinea pigs, coat colour is controlled by a single gene. The allele for black coat (B) is dominant over the allele for white coat (b). Two black-coated guinea pigs are bred together and some of their offspring have white coats. Explain how this is possible.

> WJEC GCSE Biology (Wales) — 2.3.2 Inheritance · Explain · 4 marks

## Mark scheme (4 marks)

1. Both parents must carry the recessive allele for white coat
2. Each parent can pass on either allele to their offspring
3. An offspring inherits one allele from each parent
4. An offspring with the genotype bb shows the white coat phenotype because there is no dominant allele to mask it

## Key terms

- [allele](https://www.gradenine.co.uk/glossary/allele)
- [dominant](https://www.gradenine.co.uk/glossary/dominant)

## Related

- [Revision notes for WJEC GCSE Biology (Wales)](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/in-guinea-pigs-coat-colour-is-e08cb8f1) · Published by Druglandscape Ltd.