# In pea plants, the allele for tall stems (T) is dominant over the allele for dwarf stems (t). A tall pea plant is crossed with a dwarf pea plant. All of the offspring produced are tall. Explain what the genotypes of the two parent plants must be, and why all of the offspring are tall.

> Eduqas GCSE Biology — 2.3.2 Inheritance · Explain · 4 marks

## Mark scheme (4 marks)

1. The tall parent must be homozygous dominant (TT)
2. The dwarf parent must be homozygous recessive (tt)
3. All offspring receive one T allele (from the tall parent) and one t allele (from the dwarf parent), giving genotype Tt
4. T is dominant over t, so all offspring with genotype Tt show the tall phenotype

## Key terms

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

## Related

- [Revision notes for Eduqas GCSE Biology](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/in-pea-plants-the-allele-for-4c1360cd) · Published by Druglandscape Ltd.