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

/chi·as·ma/ (ki-az´mah) pl. chias´mata   [L.] chiasm; 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.

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.

chiasma

[kī·az′mə] pl. chiasmata
Etymology: Gk, lines that cross
a visible connection between homologous chromosomes during the first meiotic division in gametogenesis. Chiasmata appear as X-shaped configurations during the late prophase stage and provide the means by which homologous chromosomes exchange genetic material. See also crossing over. chiasmatic, chiasmic, 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]

chiasma

pl. chiasmata [L., Gr.] chiasm; 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.

chiasma formation
the process by which a chiasma is formed; it is the cytological basis of genetic recombination, or crossing over.
chiasma syndrome
optic atrophy with bilateral hemianopia.
References in periodicals archive ?
mutica ([+ or -] B-chromosomes) chiasma frequency could be reduced from around 11 chiasmata per cell to less than 1 by increasing the number of B-chromosomes (Ohta, 1991).
Interestingly, the redistribution of chiasmata may be more severe in the homozygous condition than in the heterozygous one, in which chromosome similarity has actually been slightly reduced (Suja et al.
Apart from changing the frequency of chiasmata, elevated temperature has also been demonstrated to affect their localization on the chromosomes (Henderson, 1962, 1963).
When discussing the possible importance of different values describing chromosome pairing it might be of interest to look at the actual distribution of chiasmata in hybrids (Petersen & Seberg, 1996).
5 chiasmata (involving only Hordeum chromosomes) per cell (Petersen, 1991) [ILLUSTRATION FOR FIGURE 3G OMITTED].
he observed virtually no pairing and approximately 4 chiasmata per cell in hybrids, depending on which species functioned as pollen donor ([ILLUSTRATION FOR FIGURE 3E OMITTED]; Kihara, 1929).