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Sexual reproduction requires the formation of specialised sex cells — gametes — and their fusion during fertilisation to produce a new organism. The Edexcel A-Level Biology specification (9BI0) requires you to understand how gametes are formed through meiosis, the structural adaptations of sperm and egg cells, and the process of fertilisation in mammals.
Gametes are the reproductive cells (sex cells) produced by sexually reproducing organisms. They are haploid (n), meaning they contain half the number of chromosomes of the parent organism's body cells.
In mammals:
| Gamete | Produced in | Produced by | Chromosome number (human) |
|---|---|---|---|
| Sperm (spermatozoa) | Testes | Males | 23 (haploid) |
| Egg (ovum; plural: ova) | Ovaries | Females | 23 (haploid) |
When a sperm and egg fuse during fertilisation, the resulting zygote is diploid (2n) — it has the full complement of chromosomes (46 in humans).
Spermatogenesis is the process by which spermatozoa (sperm cells) are produced in the seminiferous tubules of the testes. It begins at puberty and continues throughout adult life.
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