THE MENDELIAN PRINCIPLES OF HEREDITY 89 



In the gray-red Fi female there will be the possibility 

 of interchange of the G and F, and of the W and R 

 factors, so, that gametes of four kinds will be formed, 

 namely, GRX — GWX — YRX — YWX. For the 

 moment we may assume free interchange of factors ; 

 and therefore these four classes of eggs will exist in 

 equal numbers. 



In the gray-red Fi male there is but one X chromo- 

 some that contains the factors G and R. There will 

 be then only one kind of female-producing sperm, 

 viz., GRX ; and one kind of male-producing sperm, 

 the latter containing no X, and therefore none of the 

 factors in question. The chance meeting of these two 

 classes of sperm and the four classes of eggs gives the 

 following results : 



Fi eggs GRX — GWX — YRX — YWX 

 Fi sperm GRX 



Females. Males. 



GRXGRX gray-red.— GRX gray-red. 



GRXGWX gray-red.— GWX gray-white. 



GRXYRX gray-red.— YRX yellow-red. 



GRXYWX gray-red.— YWX yellow-white. 



All the females are gray with red eyes, since these 

 are the dominant characters. There are four classes 

 of males. These males give a measure of the kinds of 

 eggs produced by the females, since the male-producing 

 sperms, having no sex chromosomes, do not affect 

 the sex-linked characters derived through the sex 

 chromosome of the Fi female. The expected proportion 

 is therefore : 



