16 



thp:ory of evolution 



other type smaller sjjlotches (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 haemoj^hilia. are transmitted as sex 

 linked characters. 





Fic. 37. Two types (if markings on tliorax of Drosophila 

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



In domestic fowls sex linked inheritance has 

 been found as the characteristic method of 

 ti'ansmission for at least as many as six char- 

 acters, but here tlie relation of the sexes is in 

 a sense reversed. For instance, if a black 

 Langshan hen is crossed to a barred Plymouth 

 Rf)ck cock (fig. 39). the offspring are all 



