Walker, Michelle Y. Department of Genetics, University of California, Davis, California.
Hawley, R. Scott Stowers Institute for Medical Research, Kansas City, Missouri.
Last reviewed:August 2019
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- Chromosome behavior
- Meiotic divisions
- Details of meiotic prophase
- Sex differences in meiosis
- Errors of meiosis
- Meiosis versus mitosis
- Related Primary Literature
- Additional Reading
The set of two successive cell divisions that serve to separate homologous chromosome pairs and thus reduce the total number of chromosomes by half. The process of meiosis (Fig. 1) includes two sequential nuclear divisions (meiosis I and II) that must occur prior to the formation of gametes [sperm and eggs (ova)]. The major purpose of meiosis is the precise reduction in the number of chromosomes by one-half, so a diploid cell (diploid = having two complete chromosome pairs in a nucleus) can create haploid gametes (haploid = having half of the diploid or full complement of chromosomes). To accomplish this reduction, a single parent cell undergoes two meiotic divisions to produce four daughter cells, with each having half of the original chromosome complement. The nonmeiotic (or somatic) cells of humans, for instance, have 46 individual chromosomes, or 23 pairs of homologous chromosomes. However, following meiosis, human eggs or sperm have only 23 chromosomes (one member of each pair). Reducing the number of chromosomes in the gametes to 23 allows the fusion of an egg with a sperm (in a process called fertilization) to result in an embryo with the requisite 46 chromosomes. Therefore, meiosis is a critical component of sexual reproduction. See also: Animal reproduction; Cell (biology); Cell biology; Cell division; Chromosome; Fertilization (animal); Fertilization (plant); Gametogenesis; Genetics; Ovum; Plant reproduction; Sperm cell
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