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 F 2 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 linked 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- 



