226 THE THEORY OF THE GENE 



The occurrence here of two red 9 's and one white male 

 may be accounted for, if, in the F x $ (X w Y r ), an inter- 

 change occurred about once out of 451 times, as shown in 

 Fig. 131. Similar results were obtained when white and 

 brown males were crossed, but no cross-overs were re- 

 corded. When variegated red females and white males 

 were crossed, the same kind of results were obtained with 

 11 cross-overs out of 172 individuals in the back-cross. 



red f^ d 



X'Y r 



crossover gametes 

 ,er m cells X" X*- Y - X*"- Y* 



F 2 xY x"Y. x"x' Yt 



white p redd* redo white d 



crossover zygotes 



Fig. 131. 



Diagram illustrating crossing-over between genes for red and for 

 white carried by the X- and ' ' Y-chromosome ' ' of an F 1 male fish. 

 These genes are interpreted as allelomorphs. 



Winge (1922-1923) extended Schmidt's experiments 

 with Lebistes, and independently reached the same con- 

 clusions concerning the Y-chromosomes as had Aida. The 

 results of a cross between a female of one race, X X , and 

 a male of another race, X e Y m , are shown in Fig. 128. The 

 ripe germ-cells of this heterozygous male are represented 

 by two non-cross-over classes, X e and Y m , and two cross- 

 over classes, X and Y em . Correspondingly there were two 



