- Mitosis/Meiosis
We saw earlier that in almost all cells of most organisms, there exists two of each type of chromosome, called homologs. This type of chromosome complement is described as diploid (2n or two of each type). Almost all Human cells contain 46 chromosomes (other organisms have different numbers) the 46 chromosomes can be arranged into 23 pairs of homologous chromosomes. In 22 of the pairs, the chromosomes match each other perfectly in appearance: these are called autosomes. The remaining pair of chromosomes are the sex chromosomes, designated X and Y.

Meiosis reduces the number of chromosomes in the cells. Gametes (e.g. sperm or egg cells) contain haploid numbers of chromosomes (called n) that is exactly half the diploid number. These gametes only contain one of each of the homologous pairs. In humans this haploid number is 23, representing +22 autosomal chromosomes plus one of the sex chromosomes. During Meiosis, homologs are distributed randomly into the gametes. This creates gametes that are genetically distinct from one another.

Fusion of the haploid male and female gametes restores the normal chromosome complement to the diploid number of 46 (n + n = 2n). Many of the mechanics of the processes of mitosis and meiosis are similar, but the outcomes are very different. To reduce the number of chromosomes, Meiosis uses two separate cell divisions (cytokinesis), in contrast to the single division in mitosis.