# Meiosis

Cell division that makes four different sex cells, each with half the usual number of chromosomes.

Biology (school) · Part 05: Genes and inheritance · Card 9 of 11 · Last updated 2026-10-19

## Analogy

Shuffling a deck and dealing half to each player.

## In practice

Meiosis happens in the ovaries and testes to make eggs and sperm.

## Practice

### Flashcards

- **How many chromosomes does a human sperm or egg have?** 23, which is half the normal number.

### Interview questions

**Compare mitosis and meiosis.**

- Mitosis makes two identical cells, meiosis makes four different cells
- Mitosis keeps the full chromosome number, meiosis halves it
- Mitosis is for growth and repair, meiosis makes gametes
- Meiosis creates variation

## Questions people ask

### Why do sex cells need half the chromosomes?

When an egg and sperm join at fertilisation, their chromosomes combine. If each had 46, the baby's cells would have 92. Halving the number to 23 in each sex cell means the fertilised egg ends up with the correct 46 chromosomes, which stays the same across generations.

### How does meiosis create variation?

During meiosis the chromosomes are shuffled, so each egg or sperm gets a random mix of the mother's and father's chromosomes. Parts of chromosomes can also swap places. Because of this, every sex cell is different, and so brothers and sisters are not identical except for identical twins.

## Related concepts

- [Mitosis](https://studyvisually.com/learn/science/biology-school/biology-school-part-5/biology-school-part-5-concept-8)
- [Chromosome](https://studyvisually.com/learn/science/biology-school/biology-school-part-5/biology-school-part-5-concept-3)

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