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chiasma Line breaks: chi|asma
Pronunciation: /kʌɪˈazmə/

Definition of chiasma in English:

noun (plural chiasmata kʌɪˈazmətəkɪˈazmətə)

1 (also optic chiasma) Anatomy The X-shaped structure formed at the point below the brain where the two optic nerves cross over each other.
Example sentences
  • The dura that invests the optic chiasma can be traced from the chiasma along the optic nerve.
2 Biology 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 sentences
  • A given factor s can affect the recombination rate r through a change in the number of chiasmata occurring during meiosis.
  • However, the observed differences may be conditional on the chromosomal location of the chiasmata.
  • First, it generates crossovers between homologous chromosomes that mature into visible chiasmata.


Mid 19th century: modern Latin, from Greek chiasma 'crosspiece, cross-shaped mark', from khiazein 'mark with the letter chi'.

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