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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 ?
All analyzed trivalents showed the same meiotic behavior in relation to frequency and distri bution of chiasmata, despite having originated from different chromosomes (Fig3b).
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.
At this stage, the autosomal bivalents normally exhibit only one or two chiasmata located in different localization: terminal, subterminal or interstitial.
A related problem was grasshopper species with strong localization of chiasmata in males.
The larger and the medium-sized bivalents may show two terminal chiasmata or a single terminal or sub-terminal chiasma; while the small bivalents only have one terminal chiasma (Figs.
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).
The point at which this crossing over occurs is known as the chiasmata.
Chromosomes average one chiasma per bivalent, which means there are, on average, as many chiasmata in every meiotic division as the haploid chromosome number.
Chromosome pairing is used to describe the occurrence of one or more chiasmata (points of attachment between homologous chromosomes resulting from crossing over) between two or more entire chromosomes or between two chromosome arms (Kimber et al.
infestans (13), the chiasmata either do not form, or form less frequently, in the euchromatic regions adjacent to the heterochromatin segments.
First, the number of chiasmata observed at metaphase may be an underestimate of crossover events.