chiasma

[ kahy-az-muh ]

noun

, plural chi·as·mas, chi·as·ma·ta [kahy-, az, -m, uh, -t, uh].

1. Anatomy. a crossing or decussation, as that of the optic nerves at the base of the brain.
2. Cell Biology. a point of overlap of paired chromatids at which fusion and exchange of genetic material take place during prophase of meiosis.

chiasma

/ kaɪˈæzmə; ˈkaɪæzəm /

noun

1. cytology the cross-shaped connection produced by the crossing over of pairing chromosomes during meiosis
2. anatomy the crossing over of two parts or structures, such as the fibres of the optic nerves in the brain

Derived Forms

• chiˈasmal, adjective

Other Words From

• chi·asmal chi·asmic chi·as·mat·ic [kahy-az-, mat, -ik], adjective

Word History and Origins

Origin of chiasma¹

1830–40; < Greek: crosspiece of wood, cross-bandage, equivalent to chi chi ¹ + -asma noun suffix

Word History and Origins

Origin of chiasma¹

C19: from Greek khiasma wooden crosspiece, from khiazein to mark with an X, from khi chi ¹

Example Sentences

Pressure on the optic chiasma, for example by a tumour of the pituitary body, is associated with bilateral temporal hemianopsia.

From Project Gutenberg

The movement follows the course of the optic nerve, traverses the chiasma, goes along the fascia, passes the internal capsule, and finally arrives at the visual centres of the occipital region.

From Project Gutenberg

They have an arterial cone and bulb, spiral intestinal valve, and the optic nerves united by a chiasma.

From Project Gutenberg

We know that they are directly connected by fibres that arch round through the chiasma.

From Project Gutenberg