# A rabbit breeder is studying fur colour in rabbits. Brown fur colour is controlled by a dominant allele (F) and white fur colour is controlled by a recessive allele (f). Two rabbits that are both heterozygous for fur colour are crossed. Explain the expected ratio of phenotypes in the offspring of this cross.

> Edexcel GCSE Biology (1BI0) — 3.4 Inheritance · Explain · 4 marks

## Mark scheme (4 marks)

1. Both parents have genotype Ff (heterozygous)
2. Correct Punnett square outcomes: FF, Ff, Ff, ff (or equivalent stated genotype ratios 1 FF : 2 Ff : 1 ff)
3. Three offspring (FF and Ff) will have brown fur because F is dominant / the dominant allele is expressed
4. One offspring (ff) will have white fur, giving an expected ratio of 3 brown : 1 white

## Key terms

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

## Related

- [Revision notes for Edexcel GCSE Biology (1BI0)](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-rabbit-breeder-is-studying-fur-39eedbca) · Published by Druglandscape Ltd.