What is Meiosis?
You already know that mitosis produces identical copies of cells for growth and repair. But how are sex cells — sperm and eggs — made? They can't be identical copies, because if they were, every time two sex cells fused during fertilisation, the chromosome number would double! This is where meiosis comes in.
A type of cell division that produces four genetically unique daughter cells, each with half the chromosome number of the parent cell. It occurs in the reproductive organs to produce sex cells (gametes).
Meiosis is sometimes called reduction division because it reduces the chromosome number by half. In humans, normal body cells contain 46 chromosomes (23 pairs). Meiosis produces gametes with only 23 chromosomes — one from each pair.
Think of meiosis like shuffling and dealing a deck of cards. You start with a full deck (46 cards/chromosomes), shuffle them thoroughly, then deal them into four separate hands of 23 cards each. Each hand is unique — no two are the same!
Meiosis takes place in the gonads — the testes (in males, producing sperm) and the ovaries (in females, producing eggs). When a sperm and egg fuse during fertilisation, the resulting zygote gets 23 chromosomes from each parent, restoring the full count of 46.
Why Meiosis Matters: Maintaining Chromosome Number
Every species has a characteristic chromosome number. Humans have 46, dogs have 78, and fruit flies have just 8. This number must stay constant from generation to generation — and meiosis is the mechanism that makes this possible.
A cell containing two complete sets of chromosomes — one inherited from each parent. Human body cells are diploid with 46 chromosomes (2n = 46).
A cell containing one set of chromosomes — half the diploid number. Human gametes are haploid with 23 chromosomes (n = 23).
The relationship between meiosis and fertilisation forms a cycle:
- Diploid parent cell (2n = 46) undergoes meiosis
- Four haploid gametes produced (n = 23)
- Two gametes fuse at fertilisation
- Diploid zygote restored (2n = 46)
Don't confuse haploid and diploid. Gametes are haploid (n). Body cells (somatic cells) are diploid (2n). After fertilisation, the zygote is diploid again. Always check which type of cell you're talking about!
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