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a cross-shaped structure commonly observed between non-sister chromatids during meiosis; the site of crossing over

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A cross-over between strands of two non-sister chromatids during recombination. The junction where two homologous chromosomes appear to exchange genetic material during recombination. (Chi is the greek letter c which resembles a genetic cross-over.) ...

Chiasma. The cross-shaped exchange configuration between non sister chromatids of homologous chromosomes that is visible during prophase I of meiosis.

chiasma The site where the exchange of chromosome segments between homologous chromosomes takes place (crossing-over) (pl.: chiasmata). PICTURE
chitin A polysaccharide contained in fungi; also forms part of the hard outer covering of insects.

~ta An X-shaped crossing formed by the crossing over of homologous chromosomes during meiosis when genetic material is exchanged.

~ pl. ~ta
The X-shaped, microscopically visible region representing homologous chromatids that have exchanged genetic material through crossing over during meiosis.
chitin ...

~ (plural ~ta): The points of physical overlap of nonsister chromatids crossing-over in meiosis.

~ - The region of physical linkage between maternal and paternal homologous pairs during genetic reassortment. Marks the location of crossover between two nonsister chromatids.
Diploid number - The total number of chromosomes present in a cell.

Optic ~ (~ opticum; optic commissure)."The optic ~ is a flattened, somewhat quadrilateral band of fibers, situated at the junction of the floor and anterior wall of the third ventricle.

Optic ~ the place where the optic nerves cross to the other side of the brain
(opti = the eye; chiasm = cross)
Organelle the "body parts" within a cell
(organum = an instrumenté implementé engine; -elle = small) ...

one or more ~ta (sing. = ~) which form between two nonsister chromatids at points where they have crossed over.
the synaptonemal complex (SC), a complex assembly of proteins (including cohesins)
At metaphase I, microtubules of the spindle fibers attach to the ...

The term which Janssens (1909) introduced for the nodes (Gk. ~; cross) where the individual chromosomes making up each pair remain in contact during the diplotene and diakinetic stages of prophase 1 and during metaphase 1 of meiosis.

~ interference: the more frequent (in the case of negative ~ interference) or less frequent (in the case of positive interference) occurrence of more than one ~ in a bivalent segment than expected by chance.

~ta separate. Chromosomes, each with two chromatids, move to separate poles. Each of the daughter cells is now haploid (23 chromosomes), but each chromosome has two chromatids.
Telophase I
Nuclear envelopes may reform, or the cell may quickly start meiosis II.

~ - the structures visible where homologous chromosomes have crossed over
chromatin - the term for chromosomes when they are relatively unwound and less visisble during interphase ...

~ A decussation or X-shaped crossing; the places where pairs of homologous chromatids remain in contact during late prophase to anaphase of the first meiotic division. The ~ indicates where an exchange of homologous segments has taken place between nonsister chromatids by crossing over.

Rees H, Dale PJ: ~ta and variability in Lolium and Festuca populations.
Chromosoma 1974, 47:335-51. Publisher Full Text
Ross-Ibarra J: The evolution of recombination under domestication: a test of two hypotheses. ...

Anaphase I: ~ta break apart and sister chromatids begin migrating toward opposite poles.
Telophase I: CLEAVAGE FURROW forms beginning the process of CYTOKINESIS (cell division). Resulting daughter cells are HAPLOID (1N).

These breakage points result in "cross-overs" or ~ta.
Metaphase I
The bivalents move to the equator of the cell. Which pair of chromosomes orientates to which pole is completely random (called random assortment.) ...

And it turns out that there are these things called ~ta, which are actually where strands of the duplicated homologous chromosomes break and recombine with the same strand of the other homolog.

At the sites where exchange happens, ~ta form. The exchange of information between the non-sister chromatids results in a recombination of information; each chromosome has the complete set of information it had before, and there are no gaps formed as a result of the process.

X-shaped regions called ~ta are visible as the physical manifestation of crossing over. Synapsis and crossing over do not occur in mitosis.
At metaphase I of meiosis, homologous pairs of chromosomes align along the metaphase plate.

Once crossing over is finnished the homologous chromosomes are no longer tightly linked however the connection between the non-sister chromatids remains, forming an X - shaped structure called a ~. The ~ links homologous chromosome pairs together and remains until late metaphase I.

Recombination: Exchange of gene segments by crossing over at ~ta (exchange of material between non-sister chromatids). The exchanged sections are usually homologous. The likelihood of recombination increases with increasing physical distance.

The chromosomes then start to move away from each other, but remain linked at points called ~ta. At this stage, some genetic material can be exchanged between chromosomes : it is now that crossing-over may take place.

(Redirected from Anaphase I) Jump to: navigation, search ... The ~ta remain on the chromosomes until they are severed in Anaphase I. ...
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During meiosis, when homologous chromosomes are paired together, there are points along the chromosomes that make contact with the other pair. This point of contact is deemed the ~ta, and can allow the exchange of genetic information between chromosomes.

A model that explains both crossing over and gene conversion by assuming the production of a short stretch of heteroduplex DNA (formed from both parental DNAs) in the vicinity of a ~.

See also: See also: What is the meaning of Homologous, Chromosome, Chromosomes, Cells, Crossing?

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