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 ?
There are suggestions that patients with less severe preoperative visual loss present the involvement of optic nerve and chiasma with tumor to a lesser degree intraoperatively [7, 15, 18].
chief executive officer of Chiasma said, "The commitment from both new and existing investors provide us with the resources to advance our regulatory efforts, prepare for a successful launch of octreotide capsules, test oral octreotide capsules for additional indications and further invest in earlier-stage TPE programs that can fuel our growth over the long term.
Since most of optic pathway gliomas are slow growing especially in children, conservative attitude is advised even if tumour is involving optic chiasma and hypothalamus6.
Securities and Exchange Commission, Chiasma lists its headquarters as Newton Center, whereas the company s website says it is based in Jerusalem, Israel, where it does its research.
Optic nerve gliomas (ONGs) are seen in 5-15% of cases, can involve one or both optic nerves and commonly extend posteriorly to involve the chiasma (Fig.
Sometimes, MRI enables visualization of deeper structures--such as the optic chiasma, pituitary stalk, and the pituitary--that are not visible on ultrasound.
Chromosomes average one chiasma per bivalent, which means there are, on average, as many chiasmata in every meiotic division as the haploid chromosome number.
The origin of the MCA was located inferior to the anterior perforated substance, posterior to the olfactory trigone and lateral to the optic chiasma.
The origin of the spinal column from the brain, the pineal body (resembling a pine cone), the structure of the eye and at least some of the cranial nerves (optic with optic chiasma, oculomotor, trigeminal, facial, auditory and hypoglossal nerves) were identified.
Also in 1976, George Butterick sent me Charles Olson's lecture notes (written in 1953) on the archaic past (published in 1978 as Olson #10: "The Chiasma, or Lectures in the New Sciences of Man").