82 SEX INHERITANCE 



have already been given ; that of white eyes is typical 

 of all the rest. The main facts may be restated 

 here. If a white eyed male is bred to a red eyed 

 female the offspring are red eyed (Fig. 9). If these 

 are inbred all of the F2 daughters are red eyed, but 

 half of the sons are white eyed and half red eyed. 

 In a word, the grandfather transmits his characters 

 visibly to half of his grandsons but to none of his 

 granddaughters. 



In the reciprocal cross (Fig. 10), a white eyed 

 female bred to a red eyed male produces the criss- 

 cross result of red eyed daughters and white eyed 

 sons. These give white and red eyed males and fe- 

 males in equal numbers. On the assumption that the 

 factor for white eyes is carried by the sex chromo- 

 somes the inheritance of white eyes can be readily 

 understood. It will be observed that a female trans- 

 mits to each of her sons one of her X chromosomes 

 with all the factors contained in it. Her sons will 

 show all of these sex hnked characters whether they 

 be dominant or recessive since they receive no other 

 X to dominate those characters and the Y contains 

 no dominant factor. For example, if a stock be 

 made up pure for yellow body color, white eyes, ab- 

 normal abdomen, bifid wings, sable body color, forked 

 spines and bar eyes, and if a female of this stock be 

 bred to a wild male, all of her sons will be yellow, 

 white, abnormal, bifid, sable, forked and bar. The 

 daughters, however, will receive not only this chro- 

 mosome from their mother, but will also receive a 

 chromosome from the wild male (their father) con- 



