OTHER METHODS OF SEX-DETERMINATION 225 



ters (Fi) will be red. If these are inbred the results are 

 shown in the next diagram (Fig. 130). White and red 

 daughters in equal numbers are expected and red sons 

 only, that are equal in number to the sum of the two 

 female classes. 



r^ red c5^ 



Fig. 130. 

 Diagram illustrating the inheritance of red and white color from 

 two Fi heterozygous male and female fish. The Y-chromosome as 

 well as the X may carry the gene for red (r). 



Thus from a red male and a white female no white 

 grandsons are expected on this formulation unless in an 

 p^^wyr red male, crossing-over between X and Y occurs 

 to give a Y^ chromosome (Fig. 131). When such a chro- 

 mosome meets an egg-carrying X"^, a white male, X'^Y'^, 

 will be produced. A white male appeared, in fact, in one 

 experiment in which an F^ heterozygous red male, X'^Y' 

 (obtained in the above experiment), was back-crossed to 

 a pure white female. The results obtained were : 



Red 9 

 2 



White ? 

 197 



Red $ 

 251 



White $ 

 1 



