# In pea plants, the allele for round seeds (R) is dominant over the allele for wrinkled seeds (r). A homozygous round-seeded plant is crossed with a homozygous wrinkled-seeded plant. Describe the genotypes and phenotypes of the offspring produced from this cross, and explain why all offspring show the same phenotype.

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

## Mark scheme (4 marks)

1. The genotype of all offspring is Rr (heterozygous)
2. All offspring have a round-seeded phenotype
3. The R allele is dominant and is always expressed when present
4. The recessive allele (r) is not expressed because there is no second recessive allele present / a dominant allele is present

## Key terms

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

## Related

- [Revision notes for Eduqas GCSE Biology](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-pea-plants-the-allele-for-49ea6dd0) · Published by Druglandscape Ltd.