Editing Meiosis (section)

==Overview==
Although the process of meiosis is related to the more general cell division process of [[mitosis]], it differs in two important respects:
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! rowspan=2 style="background: #DDEEFF;" | recombination
| meiosis
| align="center" |  [[Genetic recombination|shuffles the genes]] between the two chromosomes in each pair (one received from each parent), producing lots of recombinant chromosomes with unique genetic combinations in every gamete
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| mitosis
| align="center" | occurs only if needed to repair DNA damage;
usually occurs between identical sister chromatids and does not result in genetic changes
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! colspan=3  style="background:#dddddd;" |  &nbsp;
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! rowspan=2 style="background: #DDEEFF;" | chromosome number (ploidy)
| meiosis
| align="center" | produces four genetically unique cells, each with [[haploid|half]] the number of chromosomes as in the parent
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| mitosis
| align="center" |produces two genetically identical cells, each with [[Ploidy#Diploid|the same number]] of chromosomes as in the parent
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Meiosis begins with a diploid cell, which contains two copies of each chromosome, termed [[homologs]]. First, the cell undergoes [[DNA replication]], so each homolog now consists of two identical sister chromatids. Then each set of homologs pair with each other and exchange genetic information by [[homologous recombination]] often leading to physical connections ([[Chromosomal crossover|crossovers]]) between the homologs. In the first meiotic division, the homologs are segregated to separate daughter cells by the [[spindle apparatus]]. The cells then proceed to a second division without an intervening round of DNA replication. The sister chromatids are segregated to separate daughter cells to produce a total of four haploid cells. Female animals employ a slight variation on this pattern and produce one large ovum and three small polar bodies. Because of recombination, an individual chromatid can consist of a new combination of maternal and paternal genetic information, resulting in offspring that are genetically distinct from either parent. Furthermore, an individual gamete can include an assortment of maternal, paternal, and recombinant chromatids. This genetic diversity resulting from sexual reproduction contributes to the variation in traits upon which [[natural selection]] can act.

Meiosis uses many of the same mechanisms as [[mitosis]], the type of cell division used by [[eukaryote]]s to divide one cell into two identical daughter cells. In some plants, fungi, and [[protist]]s meiosis results in the formation of [[spore]]s: haploid cells that can divide vegetatively without undergoing fertilization. Some eukaryotes, like [[bdelloid rotifers]], do not have the ability to carry out meiosis and have acquired the ability to reproduce by [[parthenogenesis]].

Meiosis does not occur in [[archaea]] or [[bacteria]], which generally reproduce asexually via [[binary fission]].  However, a "sexual" process known as [[horizontal gene transfer]] involves the transfer of DNA from one bacterium or [[archaea|archaeon]] to another and recombination of these DNA molecules of different parental origin.