chiasma

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chiasma

(kīăz`mə): see crossing overcrossing over,
process in genetics by which the two chromosomes of a homologous pair exchange equal segments with each other. Crossing over occurs in the first division of meiosis. At that stage each chromosome has replicated into two strands called sister chromatids.
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chiasma

[kī′az·mə]
(anatomy)
A cross-shaped point of intersection of two parts, especially of the optic nerves.
(cell and molecular biology)
The point of junction and fusion between paired chromatids or chromosomes, first seen during diplotene of meiosis.
References in periodicals archive ?
4, then all other chromosome arms of the A complement pair with their B complement partner with the same frequency (Alonso & Kimber, 1981; Chapman & Kimber, 1992a); and 4) the distribution of the numbers of chiasmata is normal (Crane, 1996).
The first assumption implies that formation of chiasmata of the two arms of any chromosome is independent.
The fourth assumption requires that the number of chiasmata is normal distributed with fully populated upper and lower ends (Crane, 1996).
Many problems related to the use of the above models stem from a lack in identification of those chromosomes involved in chiasmata formation.
In the present context the most important effect of B-chromosomes is their apparent ability to change the number of chiasmata, but their ability to change the position of chiasmata may also be noteworthy in this respect (Parker et al.
those where one arm of a metacentric formed chiasmata both with its second arm and with its homologue) were found, indicating the presence of duplicate terminal segments within single chromosomes, which in turn might suggest the presence of a pair of isochromosomes.