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[kahy-az-muh] /kaɪˈæz mə/
noun, plural chiasmas, chiasmata
[kahy-az-muh-tuh] /kaɪˈæz mə tə/ (Show IPA)
Anatomy. a crossing or decussation, as that of the optic nerves at the base of the brain.
Cell Biology. a point of overlap of paired chromatids at which fusion and exchange of genetic material take place during prophase of meiosis.
Also, chiasm
[kahy-az-uh m] /ˈkaɪ æz əm/ (Show IPA)
Origin of chiasma
1830-40; < Greek: crosspiece of wood, cross-bandage, equivalent to chi chi1 + -asma noun suffix
Related forms
chiasmal, chiasmic, chiasmatic
[kahy-az-mat-ik] /ˌkaɪ æzˈmæt ɪk/ (Show IPA),
adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for chiasma


noun (pl) -mas, -mata (-mətə), -asms
(cytology) the cross-shaped connection produced by the crossing over of pairing chromosomes during meiosis
(anatomy) the crossing over of two parts or structures, such as the fibres of the optic nerves in the brain
Derived Forms
chiasmal, chiasmic, adjective
Word Origin
C19: from Greek khiasma wooden crosspiece, from khiazein to mark with an X, from khichi1
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 chiasma

"a crossing," 1832, medical Latin, from Greek khiasma "two things placed crosswise," which is related to khiasmos (see chiasmus). In cytology from 1911.

Online Etymology Dictionary, © 2010 Douglas Harper
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chiasma in Medicine

chiasma chi·as·ma (kī-āz'mə) or chi·asm (kī'āz'əm)
n. pl. or chi·as·mas, chi·as·ma·ta (-mə-tə), chi·as·ms

  1. A crossing or intersection of two tracts, as of nerves or ligaments.

  2. The point of contact between paired chromatids during meiosis, resulting in a cross-shaped configuration and representing the cytological manifestation of crossing over.

chi·as'mal or chi·as'mic or chi'as·mat'ic (-māt'ĭk) adj.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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