Fig. 73. Sex-linked Inheritance 



In a cross between red-eyed female and white-eyed male, the results are explained 

 if it is assumed that the eye pigment is determined by something (W) in the X 

 chromosome. The female produces eggs containing X chromosomes, with each of 

 which is associated the determiner, W. The male, however, produces two kinds of 

 sperms, the X and Y, neither of which carries W. In the first hybrid generation 

 every individual has red eyes because each has one X chromosome (with the pigment 

 determiner, W) from the mother. In this generation both the males and the females 

 produce two kinds of germ cells, one with the color determiner and one without; 

 the sperm cells with the X chromosomes bear the color determiner, W. In the fol- 

 lowing generation there are four possible types of individuals, two types of males and 

 two of females, but white eyes are found only among the males. From Morgan, The 

 Physical Basis of Heredity, published by J. B. Lippincott Company. 



