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 ?
Abnormalities on the subscales of the National Eye Institute Visual Function Questionnaire (NEI-VFQ 25) are seen in different neuro-ophthalmic conditions including optic neuropathy from multiple sclerosis, chiasmal defects from pituitary adenoma, and homonymous hemianopia from retrochiasmal lesions (infarct, trauma, tumor, and hemorrhage).
Evaluation of an algorithm for detecting visual field defects due to chiasmal and postchiasmal lesions: the neurological hemifield test.
Bilateral loss, can be indicative of bilateral retinal or optic nerve origin, chiasmal or retrochiasmal location.
By far the most common cause of chiasmal disorders is compression by a tumour in the region of the pituitary gland, but rare non-compressive causes including infection, inflammation, and ischaemia and toxicity are encountered.
Chiasmal Lesions, whether arising from the pituitary gland itself or the surrounding tissue, are rarely accompanied by the classic, complete bitemporal field loss (Figure 3 D).
Which of these statements about chiasmal lesions is true?