# A dog breeder is studying coat colour in Labrador dogs. Black coat colour is controlled by a dominant allele (B). Yellow coat colour is caused by the recessive allele (b). The breeder crosses a homozygous black Labrador with a yellow Labrador. Explain what the genotype and phenotype of the offspring from this cross will be.

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

## Mark scheme (4 marks)

1. The homozygous black parent has genotype BB and the yellow parent has genotype bb
2. All offspring will have the genotype Bb / heterozygous
3. All offspring will have a black coat / black phenotype
4. Because B is dominant, the B allele is always expressed / the recessive b allele is masked in the presence of B

## Key terms

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

## 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-dog-breeder-is-studying-coat-34eb6d08) · Published by Druglandscape Ltd.