Definition of chiasma in English:
chiasma
nounPlural chiasmata kʌɪˈazməkɪˈazməkaɪˈæzmə
1Anatomy
The X-shaped structure formed at the point below the brain where the two optic nerves cross over each other.
Example sentencesExamples
- The dura that invests the optic chiasma can be traced from the chiasma along the optic nerve.
2Biology
A point at which paired chromosomes remain in contact during the first metaphase of meiosis, and at which crossing over and exchange of genetic material occur between the strands.
Example sentencesExamples
- Genetic recombination is absent and no chiasmata are formed in bivalents.
- A given factor s can affect the recombination rate r through a change in the number of chiasmata occurring during meiosis.
- During meiosis, homologous chromosomes become physically connected by the formation of chiasmata.
- First, it generates crossovers between homologous chromosomes that mature into visible chiasmata.
- However, the observed differences may be conditional on the chromosomal location of the chiasmata.
Origin
Mid 19th century: modern Latin, from Greek chiasma 'crosspiece, cross-shaped mark', from khiazein 'mark with the letter chi'.