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

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

From Project Gutenberg

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

From Project Gutenberg

At the base of the section are seen the optic nerves and their chiasma.

From Project Gutenberg

The optic chiasma, where present, is involved in the floor of the thalamencephalon and forms a large, upwardly-projecting ridge.

From Project Gutenberg

The nerves are fibrous, and a commencement of the chiasma is certainly present.

From Project Gutenberg