Meiosis and genetic variation

Meiosis reduces chromosome number and helps produce cells for sexual reproduction. One round of DNA copying is followed by two divisions. Homologous chromosomes separate in the first division; sister chromatids separate in the second. Crossing over and independent assortment generate new combinations of inherited variants. In humans, a typical gamete has 23 chromosomes, compared with 46 in a typical body cell. Fertilization combines two gametes and restores the paired chromosome sets.