Home (Chiasma)

 Biology 

Home  
 
 
Home » Biology » Chiasma


 

Chiasma

Biology  Chemotaxis  Chimera

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



From Wikipedia, the free encyclopedia
Jump to: navigation, search ...

Chiasma
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.

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

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

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

Chiasma (plural chiasmata): 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.

Optic Chiasma (chiasma opticum; optic commissure)."The optic chiasma 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 chiasmata (sing. = chiasma) which form between two nonsister chromatids at points where they have crossed over.
the synaptonemal complex (SC), a complex assembly of proteins (including cohesins) ...


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.

Chiasma interference: the more frequent (in the case of negative chiasma interference) or less frequent (in the case of positive interference) occurrence of more than one chiasma 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 ...

Chiasma(ta) the point(s) at which the chromatids of homologous chromosomes cross over each other during meiosis.
Chitin a nitrogen-containing polysaccharide.

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.

Anaphase I: Chiasmata 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.) ...

When the chromosomes partially separate in late prophase, the areas where crossing over occurred remain attached and are referred to as Chiasmata (sing. chiasma). They hold the chromosomes together until they separate during anaphase.

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, chiasmata 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, ...

The occurrence of a crossing-over is indicated by a special structure, a (plural ta) since the recombined inner alleles will align more with others of the same type (e.g. a with a, B with B).

X-shaped regions called chiasmata 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 .

Recombination: Exchange of gene segments by crossing over at chiasmata (exchange of material between non-sister chromatids). The exchanged sections are usually homologous.

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 chiasmata remain on the chromosomes until they are severed in Anaphase I. ...
Full article ...

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, ...

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 chiasma.

See also: See also: Homologous, Chromosome, Chromosomes, Cells, Crossing

Biology  Chemotaxis  Chimera

 
RSS Mobile