N 



A' 



Fig. 70. Some of the various possibilities which may occur as a result of the exchanges 

 of parts of chromatids during the crossing-over phenomena associated with meiosis. Two 

 chiasmata (singular, chiasma) are shown in (A), (C), (E). Observe that homologous 

 chromosome A has split equationaliy into chromatids A and A', while homologous 

 chromosome B has divided equationaliy into B and B'. The resulting interchanges be- 

 tween respective chromatids of the original homologous chromosomes are shown in (B), 

 (D), (F). The kinetochore (place of spindle-fiber attachment) is indicated by the oval 

 or circular area to the left of the chromatids. (Modified from White: Animal Cytology 

 and Evolution, London, Cambridge University Press, 1943.) 



134 



