# Explain the role of meiosis in maintaining the chromosome number of a species during sexual reproduction.

> IB DP Biology Standard Level (2023 syllabus) — D3.1 Reproduction · Explain · 4 marks

## Mark scheme (4 marks)

1. Meiosis halves the chromosome number, producing haploid gametes (from diploid parent cells).
2. Fertilisation (fusion of two gametes) restores the diploid chromosome number in the zygote.
3. Without meiosis, fertilisation would double the chromosome number each generation, which would not be sustainable.
4. Meiosis and fertilisation therefore alternate in the sexual life cycle, ensuring the chromosome number remains constant across generations.

## Key terms

- [meiosis](https://www.gradenine.co.uk/glossary/meiosis)
- [chromosome number](https://www.gradenine.co.uk/glossary/chromosome-number)

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](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/explain-the-role-of-meiosis-in-c60ba15c) · Published by Druglandscape Ltd.