Research in Animal Breeding. 



17 



thrown. Had he then substituted for these animals bulls which 

 threw only black calves to red cows he would have broken the 

 sequence of the *' red " germ plasm and established a true- 

 breeding strain of blacks. Pedigree is a rough guide in esti- 

 mating the possibilities as to whether the black belongs to the 

 class of true-breeding blacks, or to that of the impure dominant 

 blacks, but certainty as to the nature of the animal can only be 

 arrived at by the direct test of mating to the recessive red. By 

 using only tested bulls the breeder can be sure that none but 

 blacks will appear in his herd. The true test of the purity of a 

 given animal for a given character is not in its pedigree, but 

 the nature of the germ cells that it produces. We now have a 

 reasonable explanation as to why the " pure bred " beast may 

 be nevertheless in reality an impui'e dominant. 



The relation between the animal and the germ cells that it 

 produces is the essence of Mendel's discovery, and must in 

 future form the basis, of the breeder's operations where purity 

 of breed and character is desired. Where the character depends 

 upon a single pair of factors, as in the black-red cattle case, the 

 procedure for ensuring purity is simple; and there are a number 

 of such simple cases in connection with farm live stock. Many 

 of these concern coat colours because they are evident and 

 easily worked out. The polled and horned characters in cattle 

 form such an alternative pair, the latter condition being reces- 

 sive.* Horned animals appear in polled breeds in precisely the 

 same way that reds appear in black breeds, and the procedure for 

 ensuring a herd true to the polled condition is the same as that 

 for obtaining a herd of blacks which throws no reds. Further. 

 Suffolk sheep are liable to throw inferior lambs with brownish 

 markings in place of black. Records suggest that this character 

 behaves as a simple recessive, and could be eliminated by the 

 usual procedure. 



The characters that breeders are concerned with are rarely so 

 simple and distinct as the black-red case in cattle, for the possi- 

 bilities rarely form a simple alternative paii- as ali-oady described. 

 Usually they are far more complicated, and all kinds of grada- 

 tions are possible. Hence arises the question whether such 

 complicated cases can be resolved in terms of a few^ definite 

 factors showing a similar scheme of ti*ansmission. Will the 

 general principle of heredity outlined above serve to cover the 

 more complicated cases? Is Mendelism heredity, or is there any 

 other kind of inheritance? These questions will be dealt with 

 in the next article. 



Polled aniiiuils carrying the horned character sometimes show small *• sciirs." 



B 



