chi·as·ma /kaɪˈæzmə, ki-/
  交叉
  chi·as·ma /kaɪˈæzmə, kɪ-/ 名詞
  交叉,染色體交叉點
  Chi·asm Chi·as·ma n.  Anat. A commissure; an intersection or crossing of two tracts; especially, the optic commissure, or crucial union of the optic nerves. -- Chi*as*mal a..
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  chiasma
       n : an intersection or crossing of two tracts in the form of the
           letter X [syn: chiasm, decussation]
       [also: chiasmata (pl)]