What is Meiosis?

Meiosis is a special type of cell division necessary for sexual reproduction in eukaryotes. The cells produced by meiosis are gametes or spores. In many organisms, including all animals and land plants, gametes are called sperm and egg cells.
Meiosis begins with one diploid cell containing two copies of each chromosome,one from the organism's mother and one from its father,-and produces four haploid cells containing one copy of each chromosome. Each of the resulting chromosomes in the gamete cells is a unique mixture of maternal and paternal DNA, resulting in offspring that are genetically distinct from either parent. This gives rise to genetic diversity in sexually reproducing populations. This genetic diversity can provide the variation of physical and behavioural attributes upon which natural selection can act, but, as described below in Section 6, Origin and function of meiosis, the genetic diversity may be largely a by-product of the homologous recombination that is primarily employed for its DNA repair function during meiosis.

Diagram of the stages of meiosis: two stage division of a cell, producing gametes and halving the number of chromosomes in its nucleus.
Prophase I: first phase of meiosis.
Metaphase I: second phase of meiosis.
Anaphase I: third phase of meiosis.
Telophase I: fourth phase of meiosis.
Prophase II: fifth phase of meiosis.
Metaphase II: sixth phase of meiosis.
Anaphase II: seventh phase of meiosis.
Telophase II: eight phase of meiosis.
Four cells: last phase of meiosis.