CROSSIXG-OVER 



115 



The smaller classes of grandchildren, the ex- 

 change combinations or cross-overs, can be explained 

 by an interchange taking place between the chromo- 

 somes in the hybrid (2^^i) female. This is indicated 

 in the diagram. 



Non-cros5-overs 98.5 «^ 



Cross-overs 1.5 <^o 



Fig. 50. — Cross of a female vinegar fly that has white eyes and 

 yellow wings to a wild type male with red eyes and gray wings, 

 illustrating crossing-over. 



