76 THEORY OF EVOLUTION 



other type smaller splotches (fig. 37). The 

 factors that differentiate these varieties are sex 

 linked. 



Certain types of color blindness (fig. 38) 

 and certain other abnormal conditions in man 

 such as haemophilia, are transmitted as sex 

 linked characters. 



FIG. 37. Two types of markings on thorax of Drosophila 

 repleta, both found "wild". They show sex linked inheritance. 



In domestic fowls sex linked inheritance has 

 been found as the characteristic method of 

 transmission for at least as many as six char- 

 acters, but here the relation of the sexes is in 

 a sense reversed. For instance, if a black 

 Langshan hen is crossed to a barred Plymouth 

 Rock cock (fig. 39), the offspring are all 



