chiasma

(redirected from chiasmata)
Also found in: Dictionary, Thesaurus, Medical.

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.
..... Click the link for more information.
.

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 ?
Crossing over, the formation of chiasmata, results in additional genetic recombination, thus, increasing variability.
double dagger]) Xta = chiasmata (points of attachment between chromosomes at meiosis resulting from crossing over).
the number of chiasmata, and the larger structural rearrangements (e.
The positions of all chiasmata for a chromosome pairing are drawn, ordered, and then applied to the lists of junctions of the parents, to produce a single offspring which, if it contains any immigrant genetic material, is added to the stored individuals of the next generation.
The color drawings of grasshopper bivalents and chiasmata have been continually imitated in textbooks since its publication.
standleyi is 2n = 16 (12 M + 4 t) and forms bivalents only, but with highly proximal chiasmata inhibiting any potential multivalent formation.
7% contained a single bivalent (corresponding in size to chromosome 4) with chiasmata in only one arm [ILLUSTRATION FOR FIGURE 4A-B OMITTED].
He studied the effect of external environmental factors on the frequency of recombination in grasshoppers, first by looking at the influence of temperature on chiasmata frequencies and later at the consequences of x-irradiation.
Chiasmata An intersection between two fibrous bundles.
During late prophase I, all bivalents presented a ring shape, evidencing two chiasmata per bivalent.
Assuming that, in general, at least one chiasmata must occur per chromosome, then the minimum map length of a chromosome will be 50 cM, and this formula will be valid for desired intervals up to 25 cM.