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tetrad

[te-trad] /ˈtɛ træd/
noun
1.
a group of four.
2.
the number four.
3.
Cell Biology. a group of four chromatids formed by synapsis at the beginning of meiosis.
4.
Chemistry. a tetravalent or quadrivalent element, atom, or group.
Origin
1645-1655
1645-55; < Greek tetrad- (stem of tetrás) group of four
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Based on the Random House Dictionary, © Random House, Inc. 2014.
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British Dictionary definitions for tetrad

tetrad

/ˈtɛtræd/
noun
1.
a group or series of four
2.
the number four
3.
(botany) a group of four cells formed by meiosis from one diploid cell
4.
(genetics) a four-stranded structure, formed during the pachytene stage of meiosis, consisting of paired homologous chromosomes that have each divided into two chromatids
5.
(chem) an element, atom, group, or ion with a valency of four
6.
(ecology) a square of 2 × 2 km used in distribution mapping
Word Origin
C17: from Greek tetras, from tettares four
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for tetrad
n.

1650s, from Greek tetras (comb. form tetrad-) "group of four" (see tetra-).

Online Etymology Dictionary, © 2010 Douglas Harper
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tetrad in Medicine

tetrad tet·rad (tět'rād')
n.

  1. A group or set of four.

  2. A tetravalent atom, radical, or element.

  3. A group of four chromatids formed from each of a pair of homologous chromosomes that split longitudinally during the prophase of meiosis.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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tetrad in Science
tetrad
  (tět'rād')   
  1. A four-part structure that forms during prophase I of meiosis and consists of two homologous chromosomes, each composed of two identical chromatids. During prophase I of meiosis, one chromosome exchanges corresponding segments of genetic material with the other chromosome in the tetrad in the process called crossing over. See more at meiosis.

  2. A group of four cells, as of spores or pollen grains, formed from a parent cell by meiosis. As part of the process of spermatogenesis, a spermatocyte divides into a tetrad of four spermatids, cells which go on to develop into sperm. See more at spermatogenesis.


The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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