# Explain why two parents who both have brown eyes can produce a child with blue eyes. Use the terms dominant, recessive, heterozygous and phenotype in your answer.

> Eduqas GCSE Biology — 7.2 Inheritance · Explain · 4 marks

> In humans, the allele for brown eyes (B) is dominant over the allele for blue eyes (b).

## Mark scheme (4 marks)

1. Both parents must be heterozygous (Bb), carrying one dominant and one recessive allele
2. The brown eye phenotype is expressed because B (brown) is dominant and masks the recessive b allele
3. Each parent can pass either the B or the b allele to the offspring via their gametes
4. A child who inherits the b allele from both parents will have the genotype bb and will have blue eyes, as there is no dominant allele present

## Key terms

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

## Related

- [Revision notes for Eduqas GCSE Biology](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/explain-why-two-parents-who-both-bca66436) · Published by Druglandscape Ltd.