Meiosis is a type of cell division that makes gametes, the sex cells. In humans it happens in the testes, where sperm cells are made, and in the ovaries, where egg cells are made. The stages of meiosis are not needed at GCSE, but you must know what it produces.
A normal human body cell has 46 chromosomes. When one of these cells divides by meiosis it makes four daughter cells, not two. Each daughter cell has half the number of chromosomes of the original cell, so each gamete has 23 chromosomes. A cell with half the full chromosome number is called haploid.
The four gametes are genetically different from each other and from the parent cell, because the alleles are shuffled during meiosis. When a sperm and an egg fuse at fertilisation, the full chromosome number of 46 is restored. Meiosis therefore keeps the chromosome number the same from one generation to the next, and it also gives variation in the offspring.
