# In rabbits, fur colour is controlled by a single gene. The allele for brown fur (B) is dominant over the allele for white fur (b). Two rabbits that are both heterozygous for fur colour are bred together. Describe the expected genotypes and phenotypes of the offspring produced, and explain why some offspring may have white fur even though neither parent has white fur.

> Pearson Edexcel International GCSE Biology (4BI1) — 3.2 Inheritance · Describe and Explain · 4 marks

## Mark scheme (4 marks)

1. Both parents have the genotype Bb (heterozygous)
2. Offspring genotypes are BB, Bb and bb (in a 1:2:1 ratio) / three possible genotypes identified correctly
3. Offspring with genotype BB or Bb have brown fur / three out of four offspring are expected to have brown fur
4. White fur offspring are homozygous recessive (bb) / each parent carried a recessive b allele that was not expressed / the b allele is masked by the dominant B allele in the parents

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel International GCSE Biology (4BI1)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and 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-rabbits-fur-colour-is-controlled-698280ed) · Published by Druglandscape Ltd.