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Definition of MEIOSIS
: the presentation of a thing with underemphasis especially in order to achieve a greater effect :understatement
: the cellular process that results in the number of chromosomes in gamete-producing cells being reduced to one half and that involves a reduction division in which one of each pair of homologous chromosomes passes to each daughter cell and a mitotic division — compare mitosis
: the cellular process that results in the number of chromosomes in gamete-producing cells being reduced to one half and that involves a reduction division in which one of each pair of homologous chromosomes passes to each daughter cell and a mitotic division—compare mitosis 1
Division of a gamete-producing cell in which the nucleus splits twice, resulting in four sex cells (gametes, or eggs and sperm), each possessing half the number of chromosomes of the original cell. Meiosis is characteristic of organisms that reproduce sexually and have a diploid set of nuclear chromosomes (seeploidy). Before meiosis, chromosomes replicate and consist of joined sister strands (chromatids). Meiosis begins as homologous paternal and maternal chromosomes line up along the midline of the cell. The chromosomes exchange genetic material by the process of crossing-over (seelinkage group), in which chromatid strands from homologous pairs entangle and exchange segments to produce chromatids containing genetic material from both parents. The pairs then separate and are pulled to opposite ends of the cell, which then pinches in half to form two daughter cells, each containing a haploid set (half the usual number) of double-stranded chromosomes. In the second round of meiotic division, the double-stranded chromosomes of each daughter cell are pulled apart, resulting in four haploid gametes. When two gametes unite during fertilization, each contributes its haploid set of chromosomes to the new individual, restoring the diploid number. See alsomitosis.