# A single fertilised egg cell (zygote) develops into a human embryo containing thousands of cells. Explain how mitosis allows this increase in cell number, and why all the cells produced contain the same genetic information as the zygote.

> AQA A-Level Biology (7402) — 3.2.2 Cell Replication · Explain · 5 marks

> A human zygote contains 46 chromosomes. After repeated rounds of cell division, an embryo consisting of thousands of cells is formed.

## Mark scheme (5 marks)

1. The zygote divides by mitosis (to produce new cells / to increase cell number)
2. Before division, the DNA / chromosomes are copied / replicated
3. Each daughter cell receives a full / identical copy of the DNA / 46 chromosomes
4. This process repeats many times / mitosis is repeated (to produce thousands of cells)
5. All cells are genetically identical to the zygote / to each other because each copy of the DNA is identical

## Key terms

- [mitosis](https://www.gradenine.co.uk/glossary/mitosis)
- [zygote](https://www.gradenine.co.uk/glossary/zygote)

## Related

- [Revision notes for AQA A-Level Biology (7402)](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-single-fertilised-egg-cell-zygote-e7a8d706) · Published by Druglandscape Ltd.