# A farmer breeds guinea pigs. Some guinea pigs have smooth coat and some have rough coat. The allele for rough coat (R) is dominant over the allele for smooth coat (r). Two guinea pigs, both heterozygous for coat texture, are bred together. Explain why some of their offspring are likely to have smooth coat.

> OCR GCSE Biology A: Gateway Science (J247) — B5.1 Inheritance · Explain · 4 marks

> A farmer breeds guinea pigs. Some guinea pigs have smooth coat and some have rough coat. The allele for rough coat (R) is dominant over the allele for smooth coat (r). Two guinea pigs, both heterozygous for coat texture, are bred together.

## Mark scheme (4 marks)

1. Both parents are heterozygous (Rr), so each parent carries one recessive allele (r)
2. Each parent can pass on either the R or the r allele to offspring via gametes
3. Some offspring can inherit the r allele from both parents, giving the genotype rr (homozygous recessive)
4. The smooth coat phenotype is recessive and is only expressed when two copies of the recessive allele are present (rr)

## Key terms

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

## Related

- [Revision notes for OCR GCSE Biology A: Gateway Science (J247)](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-farmer-breeds-guinea-pigs-some-14c2eab2) · Published by Druglandscape Ltd.