# In pea plants, seed shape is controlled by a single gene. The allele for round seeds (R) is dominant over the allele for wrinkled seeds (r). Two pea plants that both have round seeds are crossed. Some of their offspring have wrinkled seeds. Explain how this is possible.

> WJEC GCSE Biology (Wales) — 2.3.2 Inheritance · Explain · 4 marks

## Mark scheme (4 marks)

1. Both parent plants must carry the recessive allele for wrinkled seeds
2. The parents do not show wrinkled seeds because R is dominant over r
3. Each parent passes one allele to the offspring / alleles separate during gamete formation
4. An offspring that inherits the recessive allele from both parents (rr) will have wrinkled seeds

## Key terms

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

## Related

- [Revision notes for WJEC GCSE Biology (Wales)](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/in-pea-plants-seed-shape-is-70eba9f4) · Published by Druglandscape Ltd.