144 THE BREEDING OF ANIMALS 



tical 'breeder may base his breeding methods upon the 

 principles of segregation and dominance which are founda- 

 tion stones in the theory of mendelian inheritance. 



It will also be important to remember that to utilize 

 the mendelian principle in the breeding of animals, the 

 breeder must be dealing with contrasting characters. 

 In the larger number of cases, the useful qualities of the 

 highly improved animals of the farm are but modifica- 

 tions of characters which were already present in the 

 wild forms. The function of milk secretion is common 

 to all mammals. The domestic cow is valuable because 

 this function has, through selection and skillful mating, 

 been gradually improved. The quality of giving a small 

 quantity of milk found in the wild cow, and the quality 

 of giving a large quantity of milk as present in the highly 

 improved dairy cow, are not contrasting characters. 

 The one is but a modification of the other and is probably 

 the result of accumulated fluctuating variations which 

 have been preserved by methodical selection. It will be 

 interesting to note here some characters among animals 

 which have already been found to conform to Mendel's 

 law. 



138. The inheritance of polled and horned character 

 in cattle. Examples of Mendel's law are much more 

 frequent among plants than animals. The complicated 

 nature of animal characteristics has made it difficult to 

 trace the workings of Mendel's law so far as it is related 

 to many animal characters. It is also more difficult 

 to find contrasting characters. An exception to the 

 above must be noted in the case of the horned and polled 

 characters in cattle. Whenever a pure polled animal 

 is mated with a pure horned animal, the offspring in the 

 first generation are all polled. If the first generation 



