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 ?
b) The defect suggests a lesion that is chiasmal in origin
Most commonly a nasal defect of the optic disc may be seen, with hypopigmentation of the inferonasal retina, and these individuals may have a supero-temporal visual field defect2 that does not observe the vertical midline, which distinguishes it from a visual field defect that is due to chiasmal compression.
Gross defects such as hemianopias, which can be caused by chiasmal tumours, can be detected this way.