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tetrad

[te-trad]
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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.
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Origin of tetrad

1645–55; < Greek tetrad- (stem of tetrás) group of four
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for tetrad

Historical Examples

  • The tetrad for the perfect figure—the cube, length, depth, and width.

    Notes and Queries for Worcestershire

    John Noake

  • Having sent for that Brhman, he learnt from him a tetrad of gths.

  • They are aborting members of the tetrad, and appear to have been used as food by the other spores.

    Ancient Plants

    Marie C. Stopes

  • Such an axis of symmetry is known as a tetrad axis of symmetry.

  • If the second cell division plane is formed at right angles to the first, a cell surface or tetrad is formed.


British Dictionary definitions for tetrad

tetrad

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
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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

Word Origin and History for tetrad

n.

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

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Online Etymology Dictionary, © 2010 Douglas Harper

tetrad in Medicine

tetrad

(tĕtrăd′)
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.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

tetrad in Science

tetrad

[tĕtrăd′]
  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.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.