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 (kī-ăz′mə) also chi·asm (kī′ăz′əm)
n. pl. chi·as·ma·ta (-mə-tə) or chi·as·mas also chi·asms
1. Anatomy A crossing or intersection of two tracts, as of nerves or ligaments.
2. Genetics The point of contact between paired chromatids during meiosis, resulting in a cross-shaped configuration and representing the cytological manifestation of crossing over.

[Greek khīasma, cross-piece, from khīazein, to mark with an X, from khei, khī, chi (from the letter's shape).]

chi·as′mal, chi·as′mic, chi′as·mat′ic (-măt′ĭk) adj.


(kaɪˈæzmə) or


n, pl -mas, -mata (-mətə) or -asms
1. (Genetics) cytology the cross-shaped connection produced by the crossing over of pairing chromosomes during meiosis
2. (Anatomy) anatomy the crossing over of two parts or structures, such as the fibres of the optic nerves in the brain
[C19: from Greek khiasma wooden crosspiece, from khiazein to mark with an X, from khi chi1]
chiˈasmal, chiˈasmic adj


(kaɪˈæz mə)

also chi•asm

(ˈkaɪ æz əm)

n., pl. -as•mas, -as•ma•ta (-ˈæz mə tə) also -asms.
1. Anat. a crossing or decussation. Compare optic chiasma.
2. a point of overlap of paired chromatids at which fusion and exchange of genetic material take place during prophase of meiosis.
[1830–40; < Greek: crosspiece of wood, cross-bandage =chi chi + -asma n. suffix]
chi•as′mal, chi•as′mic, chi`as•mat′ic (-ˈmæt ɪk) adj.
ThesaurusAntonymsRelated WordsSynonymsLegend:
Noun1.chiasma - an intersection or crossing of two tracts in the form of the letter X
anatomical structure, bodily structure, body structure, complex body part, structure - a particular complex anatomical part of a living thing; "he has good bone structure"
chiasma opticum, optic chiasm, optic chiasma - the crossing of the optic nerves from the two eyes at the base of the brain


, chiasma
n. quiasma.
1. cruzamiento de dos vías o conductos;
2. punto de cruzamiento de las fibras de los nervios ópticos.
References in periodicals archive ?
David Lo Pan, A Moment of Clarity, Black Hand, the Last Impression, Within a Lifetime, Chiasmata, Votes Most Random, Longshot, the Donnor Party, Kerrigan and Impulse at 6 p.
In diplotene--metaphase I plates (n = 19), we observed at least one bivalent with two chiasmata and maximally four bivalents with two chiasmata.
Therefore, SCP3 is required for chiasmata formation for the structural integrity of meiotic chromosomes and absence of SCP3 promoted aneuploidy due to altered chromosomal structure and triggering non-disjunction of chromosome (17).
infestans (13), the chiasmata either do not form, or form less frequently, in the euchromatic regions adjacent to the heterochromatin segments.
And since metaphase pairing is related to pachytene pairing through the formation of chiasmata, in the frequency of which species and varieties differ genetically, the indication becomes even more uncertain" (Darlington, 1937: 171).
In these cells, most of the bivalents possessed an interstitial chiasma with a cross configuration, with the exception of bivalents 1 and 2 that showed two chiasmata, assuming a ring configuration.