Meiosis demystified: Summary

Diploid organisms contain two copies of each gene in each of their cells. In sexual reproduction, gametes are formed containing one copy of each gene. Each offsping receives two copies of each gene, one from each of its parents.

Gametes are haploid cells, and they are formed from diploid cells by meiosis. Meiosis consists of two divisions. The first division, meiosis I, separates the homologous chromosomes, so that each cell now has only one of each pair. The second division, meiosis II, separates the chromatids of each chromosome. Meiotic division therefore produces four cells, each with one complete set of chromosomes.

The cell produced by meiosis are genetically different from each other and from their parent cell. This results from independent assortment of the chromosomes as the bivalents line up on the equator during metaphase I, and also from crossing over between the chromatids of homologous chromosomes during prophase I.

Genetic variation also results from random fertilisation, as gametes containing different varieties of genes fuse together to form a zygote.