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Definition: meiosis from The Penguin Dictionary of Psychology

The cell-division process in the formation of gametes. The products of meiosis (sperms and ova) are haploid cells containing half the full complement of chromosomes found in diploid cells. Meiosis consists of two successive cell divisions which superficially resemble MITOSIS, but the chromosomes are duplicated only once, with each daughter cell ending up with the haploid number.


meiosis

From The Columbia Encyclopedia
(mīŏ'sĭs), process of nuclear division in a living cell by which the number of chromosomes is reduced to half the original number. Meiosis occurs only in the process of gametogenesis, i.e., when the gametes, or sex cells ( ovum and sperm ), are being formed. Because fertilization consists of the fusion of two separate nuclei, one from each of the sex cells, meiosis is necessary to prevent the doubling of the chromosome number in each successive generation. An ordinary body cell is diploid; i.e., it contains two of each type of chromosome. The members of each pair are known as homologous chromosomes. An ovum or sperm is haploid; i.e., it contains only a single chromosome of each type and, therefore, half the number of chromosomes of the diploid cell. When the two haploid cells fuse, the diploid number is restored, and the plant or animal growing from the fertilized egg (zygote) has the usual diploid number of chromosomes in its cells. Just before meiosis each chromosome replicates to…
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Full text Article Meiosis

From Brenner's Encyclopedia of Genetics
Mitotic vs. meiotic cell division....
Abstract Meiosis is a feature of sexual reproduction that results in the independent assortment of genetic material from two individuals, providing greater genetic diversity. The initiation of meiosis requires both intrinsic and extrinsic signals. Meiosis is characterized by one round of DNA…
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Full text Article meiosis

From The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide
In biology, a process of cell division in which the number of chromosomes in the cell is halved. It only occurs in eukaryotic cells, and is part of a life cycle that involves sexual reproduction because it allows the genes of two parents to be combined without the total number of chromosomes…
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Full text Article MEIOSIS

From The Princeton Encyclopedia of Poetry and Poetics
(Gr., "lessening"; Lat. extenuatio) . A figure employing understatement, usually to convey that a thing is less in importance (or size) than it really is; the opposite of auxesis . Meiosis is often confused with *lito- tes, which, properly understood, affirms or increases the importance, usually by…
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Full text Article meiosis

From Dictionary of Developmental Biology and Embryology
Phases of meiotic cell...
one of two general types of cell divisions undergone by eukaryotic cells; an integral part of sexual reproduction. It was J. B. Farmer, who in a paper with J. E. Moore in 1905, proposed the name meiosis based on a greek verb, to lessen; their form of the term was spelt “maiosis,” which was altered…
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Full text Article meiosis

From Britannica Concise Encyclopedia
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…
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Full text Article meiosis

From Encyclopedia of Evolution
Meiosis consists of two divisions. In human...
Eukaryotic cells have nuclei that contain chromosomes. Chromosomes are the structures that contain DNA. When a cell reproduces itself, the chromosomes of its nucleus replicate, then the rest of the cell divides. There are two types of cell and nuclear division. In mitosis, two cells result, which…
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Full text Article meiosis

From The Columbia Encyclopedia
(mīŏ'sĭs), process of nuclear division in a living cell by which the number of chromosomes is reduced to half the original number. Meiosis occurs only in the process of gametogenesis, i.e., when the gametes, or sex cells ( ovum and sperm ), are being formed. Because fertilization consists of the…
| 320 words
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Full text Article meiosis

From The American Heritage Student Science Dictionary
meiosis
The type of cell division that produces sex cells (or sometimes spores) in animals, plants, fungi, and many algae, in which the number of chromosomes is reduced to half the original number. The first division of meiosis involves replication of the chromosomes, followed by recombination, during which…
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Full text Article Meiosis

From Black's Medical Dictionary, 43rd Edition
The formation of gametes. Top, normal meiosis....
A reduction division that is the form of cell division that only occurs in the testis (see TESTICLE ) and the ovary (see OVARIES ) – giving rise to the germ cells (gametes) of the sperms (see SPERMATOZOON ) and the ova (see OVUM ). Ova produced by normal meiosis have 22 autosomes and an X sex…
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Full text Article meiosis

From The Penguin Dictionary of Science
meiosis in a diploid cell with a pair of...
The process of cell division that results in the formation of ➤ haploid cells from ➤ diploid cells to produce, for example, ➤ gametes (see the diagram below). Meiosis also produces new combinations of genes in the nuclei of the resultant cells. Unlike ➤ mitosis , meiosis consists of two sequential…
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