Heredity — Genetics 701 



in the former, however. Sex linkage has been observed in fishes, poultry, 

 silkworms, plants, fruit flies, man, etc. 



In the fruit fly (Drosophilia) the gametes are heterozygous in the males 

 and homozygous in the females. White eyes are sex-linked characters 

 which are recessive to the normal red eyes. 



Fig. 346. — Sex-linked inheritance in the fruit fly (Drosophila sp.J. The white- 

 eyed male (upper right) and the red-eyed female (upper left) are crossed to pro- 

 duce the male and female of the Fi generation. The factor (W) for red eyes is 

 carried in the X chromosomes of the female. The factor (w) for white eyes is 

 carried in the X chromosome of the male. The curved male Y chromosome does 

 not carry an eye-color factor. When the members of the Fi generation are crossed, 

 the members of the Fo generation are produced, as shown in the lower line. Note 

 that a male has a larger tip of black on his abdomen than the female. Contrast 

 these results with those in Fig. 345. (From Morgan: Evolution and Genetics, 

 Princeton University Press.) 



