HEEEDITY AND SEX 



Second case. 



Gametes of white-eyed female = X and X, 

 Gametes of red-eyed male = X-R and — , 

 Zygotes = XX-R (red-eyed female), and — "X 

 (white-eyed male). 



A short condition of the wings in Drosophila, 

 which renders the animal incapable of flight, 

 is likewise sex-limited in heredity, as has been 

 shown by Morgan. By crossing two races of 

 Drosophila, each of which possessed a different 

 sex-limited character, Morgan has been able to 

 combine the two characters in a single race. 

 Thus was obtained a race both white-eyed and 

 short-winged. The synthesis cannot be made 

 originally in a male individual, but only in a 

 female. For only in the female can the two 

 characters be brought together, each associated 

 with a different X, since in the male only one 

 X is present. Although each sex-limited char- 

 acter seems to be attached to or bound up with 

 an X structure, it evidently has a material basis 

 distinct from X. Otherwise it would not be 

 possible for the character to leave one X and 

 attach itself to the other, as apparently takes 

 place in the female when the combination of 



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