chiasma

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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.
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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 ?
The direct pupillary photomotor reflex absence in the right eye and indirect reflex absence in both eyes can be explained by the presence of the tumor mass extending from the adjacent ocular bulb portion to the optic chiasm (Figure 1B).
Description of the Specific Measurements of the Optic Chiasm Position Relative to the Plane of the Diaphragm Sella.
Unfortunately, neurosurgery could not be delayed due to mass effect of the underlying lung adenocarcinoma metastases on the pituitary and overlying optic chiasm. Had surgery been delayable, a far less invasive diagnostic test for T790M mutation could have been performed.
Rorke et al., "Gangliogliomas involving the optic chiasm," Neurology, vol.
Retinal axons exit the eye and extend ventrally to cross the midline at the optic chiasm. They continue to extend dorsally and posteriorly to the tectum.
In addition, the manipulation and retraction of the optic nerve and the optic chiasm are reduced by adopting a medial-to-lateral trajectory in ETA.
[On (the other) half of her] he placed earth as a cover and established it firmly," where parallelism and chiasm are both semantic and syntactic (see Seri 2012: 23).
After 30 months, radiographic imaging demonstrated a reduction and stabilization of the tumors in the optic chiasm, hypothalamus, and left optic nerve.
Ischemic optic neuropathy (ION) refers to infarction of any portion of the optic nerve from the chiasm to optic nerve head.
Local anesthetic is subsequently transported towards the optic chiasm and brainstem.
It measures 4.7 mm at the level of the optic chiasm. The pituitary gland is within normal limits (asterisk).
Given the proximity of the lesion to the optic chiasm and lack of progression, a biopsy or resection was deferred to spare the risk of vision loss.