Akademik

Meiosis
What chromosomes do during germ cell formation to halve the chromosome number from 46 to 23. Chromosomes are the carriers of DNA, the hereditary material, in the cells of the body. The chromosomes are visible under the microscope. Women and men usually have 2 sex chromosomes. Women usually inherit 2 X chromosomes — one from each parent. Men usually inherit an X chromosome from their mother, and a Y chromosome from their father. In meiosis, the 46 chromosomes in the cell divide to make two new cells with 23 chromosomes each. Before meiosis is completed, however, chromosomes pair with their corresponding chromosomes and exchange bits of genetic material. In women, X chromosomes pair; in men, the X and Y chromosome pair. After the exchange, the chromosomes separate, and meiosis continues.
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A special process of cell division comprising two nuclear divisions in rapid succession that result in four gametocytes, each containing half the number of chromosomes found in somatic cells. SYN: meiotic division. [G. m., a lessening]

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mei·o·sis mī-'ō-səs n, pl mei·o·ses -.sēz 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)
mei·ot·ic mī-'ät-ik adj
mei·ot·i·cal·ly -i-k(ə-)lē adv

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(reduction division)
n.
a type of cell division that produces four daughter cells, each having half the number of chromosomes of the original cell. It occurs before the formation of sperm and ova and the normal (diploid) number of chromosomes is restored after fertilization. Meiosis also produces genetic variation in the daughter cells, brought about by the process of crossing over. Meiosis consists of two successive divisions, each divided into four stages (see prophase, metaphase, anaphase, telophase). Compare mitosis.
• meiotic adj.

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mei·o·sis (mi-oґsis) [Gr. meiōsis diminution] a special type of cell division occurring in the maturation of germ cells, consisting of two successive cell divisions (meiosis I and meiosis II) without an interval of DNA replication, by means of which diploid germ cells (primary spermatocytes and oocytes) give rise to haploid gametes. During meiosis I, homologous chromosomes are paired and segregated, resulting in a haploid number of paired chromatids; during meiosis II the paired chromatids are separated. See illustration. Cf. mitosis. meiotic adj

Meiosis (only two of the 23 human chromosome pairs are shown, the chromosomes from one parent in blue, those from the other parent in pink).


Medical dictionary. 2011.