chiasma Definition

chiasma
noun chiasmas, chiasmata

1. genetics.
During meiosis: any region where homologous chromosomes remain in contact after they have begun to separate from each other, and where mutual exchange of genetic material occurs as a result of crossing over.
2. anatomy.
The point where the optic nerves cross each other in the brain.

Etymology: 19c: Greek, meaning ‘a cross-shaped mark'.