Explain why the cells produced by meiosis must have half the number of chromosomes compared to the parent cell.

WJEC GCSE Biology (Wales) — 2.2.1 Mitosis and meiosis · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Sexual reproduction in humans involves the fusion of a sperm cell and an egg cell to form a fertilised egg called a zygote.

Model answer (4 marks)

Meiosis produces gametes that are haploid.
At fertilisation a sperm and an egg fuse.
If the gametes were not haploid the zygote would contain twice the normal chromosome number.
Having half the chromosome number in each gamete ensures the zygote is diploid and has the correct chromosome number.

Examiner tips

Use the word ‘haploid’ and ‘diploid’ – examiners look for correct terminology.
Show the logical sequence: meiosis → haploid gametes → fertilisation → diploid zygote.
Keep the answer concise – one sentence per point.
Mention fertilisation explicitly to link to the question.

Common mistakes

Using ‘diploid’ for the gametes instead of ‘haploid’.
Omitting the step that fertilisation restores the diploid number.
Writing a long paragraph instead of clear, separate points.

Mark scheme (4 marks)

Meiosis produces gametes (sperm and egg cells)
At fertilisation, a sperm and egg cell fuse / join together
If gametes were not haploid, the zygote would have double the normal chromosome number
Having half the chromosome number (haploid) in each gamete means the zygote has the correct / normal chromosome number (diploid) after fertilisation

Key terms in this question

meiosis