Some Apparent Exceptions 97 



Another apparent exception to Mendel's 

 law is the inheritance of sex-linked characters, 

 but it also is explicable on the supposition that 

 the factor or factors that determine the char- 

 acter are contained in the sex chromosome. 

 In fruit flies, reared in Professor Morgan's 

 laboratory, there appeared a sport with white 

 eyes. The normal fly has red eyes. The 

 factor for red in the eye, it is supposed, is 

 carried by the sex chromosome. We may 

 represent the sex chromosome by • and show 

 the presence of the red factor by making it 

 black, its absence by leaving it imcolored, o . 

 Since the female has a double dose of the sex 

 chromosome, the male a single dose, a cross 

 of the red-eyed male and the white-eyed female 

 would be represented thus : 



White-eyed female DO) [#1 Red-eyed male 



Eggs all alike (Pi) ^ Sperm of two sorts 



The offspring in the Fj generation would be of 

 two sorts, @ [o]; the left-hand diagram repre- 

 senting the red-eyed females, the right-hand 

 the white-eyed males. There wiU be equal 



