Meiosis

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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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.

Look at other dictionaries:

  • Meiosis — es una de las formas de la reproducción celular. Este proceso se realiza en las glandulas sexuales para la produccion de gametos. Es un proceso de división celular en el cual una célula diploide (2n) experimenta dos divisiones sucesivas, con la… …   Wikipedia Español

  • meiosis — f. citol. División celular propia de las células germinales durante el proceso de maduración que transformará la ovogonia en ovocito y la espermatogonia en espermatocito. Se trata de una división reduccional, es decir, una división celular en la… …   Diccionario médico

  • meiosis — division of a cell nucleus, 1905, from Gk. meiosis a lessening, from meioun to lessen, from meion less, from PIE root *mei small (see MINUS (Cf. minus)). Earlier (1580s) it was a rhetorical term, a figure of speech weak or negative expression… …   Etymology dictionary

  • meiosis — pronounced miy oh sis, is a figure of speech involving an emphatic understatement made for effect, as when something outstanding is described as ‘rather good’. A literary example occurs in Shakespeare s Romeo and Juliet, where Mercutio refers to… …   Modern English usage

  • meiosis — o meyosis sustantivo femenino 1. Área: biología Proceso de división celular por el cual, a partir de una célula madre, se originan cuatro células hijas o gametos y se reduce el número de cromosomas a la mitad: La meiosis está presente en el… …   Diccionario Salamanca de la Lengua Española

  • meiosis — [mī ō′sis] n. [ModL < Gr meiōsis < meioun, to make smaller < meiōn, less: see MINOR] 1. the process of two consecutive nuclear divisions in the formation of germ cells in animals and of spores in most plants, by which the number of… …   English World dictionary

  • Meiosis — Mei*o sis (m[ i]*[=o] s[i^]s), n. [NL., fr. Gr. mei wsis, fr. meioy^n to make smaller, from mei wn. See {Meionite}.] 1. (Rhet.) Diminution; a species of hyperbole, representing a thing as being less than it really is; understatement; see also… …   The Collaborative International Dictionary of English

  • meiosis — meiosis. См. деление созревания. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • Meiōsis — (gr.), 1) krankhafte Verkleinerung eines Theils; 2) so v.w. Myosis; 3) rhetorische Figur, die, scheinbar verkleinernd, vergrößert; z.B. Abraham war nicht schwach (d.i. sehr stark) im Glauben …   Pierer's Universal-Lexikon

  • Meiosis — Meiosis, griech. = Verminderung, rhetorische Figur, wobei man sich eines scheinbar verringernden Ausdrucks bedient, um den Gegenstand schärfer hervorzuheben …   Herders Conversations-Lexikon

  • meiosis — (Del gr. μείωσις, disminución). f. Biol. Sucesión de dos divisiones celulares durante la formación de los gametos, de la que resultan cuatro células que tienen un cromosoma de cada pareja de la célula original …   Diccionario de la lengua española

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