chiasma

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chiasma

 [ki-az´mah] (pl. chias´mata) (L.; Gr.)
in genetics, the points at which members of a chromosome pair are in contact during the prophase of meiosis and because of which recombination, or crossing over, occurs on separation. See also chiasma formation.

chi·asm

(kī'azm),
1. An intersection or crossing of two lines.
2. In anatomy, a decussation or crossing of two fibrous bundles, such as tendons, nerves, or tracts.
3. In cytogenetics, the site at which two homologous chromosomes make contact (thus appearing to be crossed), enabling the exchange of genetic material during the prophase stage of meiosis.
Synonym(s): chiasma [TA]
[G. chiasma]

chiasma

(kī-ăz′mə) also

chiasm

(kī′ăz′əm)
n. pl. chias·mata (-mə-tə) or chias·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.

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

chi·asm

(kīazm)
1. An intersection or crossing of two lines.
2. anatomy a decussation or crossing of two fibrous bundles, such as tendons, nerves, or tracts.
Synonym(s): chiasma.
3. cytogenetics the site at which two homologous chromosomes make contact (thus appearing to be crossed), enabling the exchange of genetic material during the prophase stage of meiosis.
Synonym(s): Budd syndrome.
[G. chiasma]

chiasma

1. The intersection and partial crossing of the optic nerves behind the eyes within the skull. The fibres on the outer halves of each optic nerve do not cross over; those on the inner halves of each nerve do. Also known as the optic chiasm.
2. The site at which a pair of homologous chromosomes exchange material during MEIOSIS.

chiasma

(pl. chiasmata) the cross-shaped configuration produced during CROSSING OVER; for example, between CHROMATIDS in MEIOSIS.

chi·asm

, chiasma (kīazm, kī-azmă)
In anatomy, decussation or crossing of two fibrous bundles, such as tendons, nerves, or tracts.
[G. chiasma]
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.
However, chiasmal involvement was seen in only one patient who was negative for both anti-AQP4 antibody and CSF OCB (Figure 3).
Yen, "Chiasmal optic neuritis: a report of three cases," Taiwan Journal of Ophthalmology, vol.
Uni- and bi-temporal visual fields defects, including those obeying the midline, need to be considered as indicative of chiasmal lesions.
One should always check the VF from the 'uninvolved' eye for subtle defects even when symptoms are unilateral (such as in the case of a temporal defect in junctional scotoma that could arise from a chiasmal compressive lesion).
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.