GENETICS AND BREEDING 171 



(6) That specific characters or groups of char- 

 acters, in the great majority of cases and perhaps 

 all, are inherited as discrete and definite units. 

 If one mates a pea-combed fowl with a single- 

 combed fowl, all the offspring will have pea-combs. 

 This result occurs whether the pea-combed parent 

 is a Game or a Brahma ; whether it is a male or a 

 female; whether it is a strong, vigorous individ- 

 ual, or the sickliest, weakest scrub in the flock. 

 In other words, the hind of a bird it is whose germ 

 cells carry the potentiality to make pea-combs 

 develop in the offspring, so far as we now know, 

 has nothing to do with the specific result (i.e., the 

 production of a pea-comb, rather than a single, a 

 rose, or any other kind). Comb form is inherited 

 as a discrete unit largely, if not completely, 

 uninfluenced by the individual's other attributes. 

 This discovery that many characters are inherited 

 as separate units — and no principle of genetics 

 is more firmly grounded than this — gives the 

 breeder a totally new concept of the meaning 

 of "purity" of blood in breeding. We see now 

 that properly (i.e., biologically) one can only 

 speak of an animal as being "pure-bred" when 

 he specifies the particular character to which he 

 refers. A chick may be the veriest mongrel in 

 all other respects and yet carry in the germ cells 

 only that potentiality in respect of comb form 

 which leads to the development of a pea-comb. 

 Then however much of a mongrel it may be in 



