In biology, meiosis is the process by which one diploid eukaryotic cell divides to generate four haploid cells often called gametes. Meiosis is essential for sexual reproduction and therefore occurs in all eukaryotes (including single-celled organisms) that reproduce sexually.

A few eukaryotes, notably the Bdelloid rotifers, have lost the ability to carry out meiosis and have acquired the ability to reproduce by parthenogenesis.

Meiosis does not occur in archaea or bacteria, which reproduce via asexual processes such as mitosis or binary fission. During meiosis, the genome of a diploid germ cell, which is composed of long segments of DNA packaged into chromosomes, undergoes DNA replication followed by two rounds of division, resulting in haploid cells called gametes.

Each gamete contains one complete set of chromosomes, or half of the genetic content of the original cell.

These resultant haploid cells can fuse with other haploid cells of the opposite sex or mating type during fertilization to create a new diploid cell, or zygote.

Thus, the division mechanism of meiosis is a reciprocal process to the joining of two genomes that occurs at fertilization.

Because the chromosomes of each parent undergo genetic recombination during meiosis, each gamete, and thus each zygote, will have a unique genetic blueprint encoded in its DNA.

In other words, meiosis and sexual reproduction produce genetic variation. Meiosis uses many of the same biochemical mechanisms employed during mitosis to accomplish the redistribution of chromosomes.

There are several features unique to meiosis, most importantly the pairing and genetic recombination between homologous chromosomes..

For more information about the topic Meiosis, read the full article at Wikipedia.org, or see the following related articles:

Biological life cycle — A life cycle is a period involving one generation of an organism through means of reproduction, whether through asexual reproduction or sexual ...  > read more

Somatic cell — A somatic cell is generally taken to mean any cell forming the body of an organism. Somatic cells, by definition, are not germline cells. In mammals, ...  > read more

Spore — In biology, a spore is a reproductive structure that is adapted for dispersion and surviving for extended periods of time in unfavorable conditions. ...  > read more

Chromosomal crossover — Homologous recombination is the process by which two chromosomes, paired up during prophase 1 of meiosis, exchange some distal portion of their DNA. ...  > read more

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