# A plant can produce either red flowers or white flowers. Red flower colour is controlled by a dominant allele (R). White flower colour is controlled by a recessive allele (r). Two plants that are heterozygous for flower colour are crossed. Explain why some of the offspring from this cross will have white flowers.

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

> Flower colour in a particular plant species is controlled by a single gene with two alleles. Red flower colour is dominant over white flower colour.

## Mark scheme (4 marks)

1. Both parent plants have the genotype Rr (heterozygous)
2. Each parent can pass on either the R allele or the r allele to offspring
3. Some offspring will inherit the r allele from both parents, giving the genotype rr
4. The white phenotype is only expressed when two copies of the recessive allele are present (rr), so rr offspring have white flowers

## Key terms

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

## 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-plant-can-produce-either-red-0c6b5fdb) · Published by Druglandscape Ltd.