Meiosis was discovered and described for the first time in sea urchin eggs in 1876, by noted German biologist Oscar Hertwig (1849-1922). 3 Occurrence of meiosis in eukaryotic life cycles.Meiosis comes from the root -meio, meaning less. There are several features unique to meiosis, most importantly the pairing and genetic recombination between homologous chromosomes. Meiosis uses many of the same biochemical mechanisms employed during mitosis to accomplish the redistribution of chromosomes. In these groups, gametes are produced by mitosis. In all plants, and in many protists, meiosis results in the formation of haploid cells that can divide vegetatively without undergoing fertilization, referred to as spores.
Together, meiosis and fertilization constitute sexuality in the eukaryotes, and generate genetically distinct individuals in populations. 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. Thus, the division mechanism of meiosis is a reciprocal process to the joining of two genomes that occurs at fertilization. If meiosis produces gametes, these cells must fuse during fertilization to create a new diploid cell, or zygote before any new growth can occur. Each of these cells contain one complete set of chromosomes, or half of the genetic content of the original cell. Meiosis does not occur in archaea or bacteria, which reproduce via asexual processes such as binary fission.ĭuring 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 four haploid cells. 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 is essential for sexual reproduction and therefore occurs in all eukaryotes (including single-celled organisms) that reproduce sexually. In animals, meiosis always results in the formation of gametes, while in other organisms it can give rise to spores. In biology or life science, meiosis (pronounced my-oh-sis) is a process of reductional division in which the number of chromosomes per cell is cut in half. Risk calculators and risk factors for MeiosisĮvents involving meiosis, showing chromosomal crossover US National Guidelines Clearinghouse on Meiosis Articles on Meiosis in N Eng J Med, Lancet, BMJ
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