226 THE THEORY OF THE GENE 



The occurrence here of two red 5 's and one white male 

 may be accounted for, if, in the F^$ (X^Y'), 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 



crossover (gametes 



w . ,r , ,r . ,w 



erm cells X X-Y-X" Y 



F2 



white p redd* redo white o 



crossover z.\jqoTe.s 

 Fig. 131. 

 Diagram illustrating crossing-over between genes for red and for 

 white carried by the X- and " Y-chromosome " of an Fj 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, XoX^, and 

 a male of another race, XeY„, are shown in Fig. 128. The 

 ripe germ-cells of this heterozygous male are represented 

 by two non-cross-over classes, Xe and Y^, and two cross- 

 over classes, Xo and Ye^. Correspondingly there were two 



