;Chiasm ( also Chiasma ) : Amounts to much the same as "'decussation "', an X-shaped crossing of nerve fibres between the cerebral hemispheres.
22.
In an " MSH4 " mutant of rice, chiasma frequency was dramatically decreased to about 10 % of the wild-type frequency, although the synaptonemal complex was normally installed.
23.
In these cells chiasma occurs and sister chromatids are partly held together by cohesions; when cell division occurs, the sister chromatids are sheared and mis-segregated which results in an aneuploid state.
24.
These results suggest that X-rays induce DNA damages, likely including double-strand breaks, and these damages are repaired by a crossover pathway leading to chiasma formation ( see Chromosomal crossover ).
25.
Visual information is then sent to the brain from retinal ganglion cells via the optic nerve to the optic chiasma : a point where the two optic nerves meet and information from the temporal ( contralateral ) visual field crosses to the other side of the brain.
26.
Experiments have been carried out with " G . australasiae " to study the time of genetic recombination in relation to the sequence of stages in meiosis, the relationship of homologous chromatids, and each such exchange event results in the formation of a cytologically visible chiasma.
27.
This surface is bounded behind by a ridge, which forms the anterior border of a narrow, transverse groove, the prechiasmatic groove, above and behind which lies the optic chiasma; the groove ends on either side in the optic foramen, which transmits the optic nerve and ophthalmic artery into the orbital cavity.
28.
The phenomenon of genetic chiasmata ( " chiasmatypie " ) was discovered and described in 1909 by Frans Alfons Janssens, a Professor at the University of Leuven in Belgium . " Bivalent " refers to the two homologous chromosomes ( 4 chromatids ); " chiasma " refers to the actual break of the phosphodiester bond during crossing over.
29.
Occupying the posterior part of the commissure of the optic chiasma is a strand of fibers, the "'Ventral supraoptic decussation "'( "'commissure of Gudden "', "'Gudden's inferior commissure "'), which is not derived from the optic nerves; it forms a connecting link between the medial geniculate bodies.
30.
The superior surface of the sphenoid bone is bounded behind by a ridge, which forms the anterior border of a narrow, transverse groove, the chiasmatic groove ( optic groove ), above and behind which lies the optic chiasma; the groove ends on either side in the optic foramen, which transmits the optic nerve and ophthalmic artery ( with accompanying sympathetic nerve fibres ) into the orbital cavity.
