ANIMAL BREEDING 



521 



379. The problem of animal breeding. Every domestic spe- 

 cies has many more or less distinct varieties. In fact, the out- 

 ward differences between two breeds of dogs or horses, for 

 example, may be greater than we sometimes observe between 

 two distinct species. The breeder's problem is, first of all, to 

 find the variety or breed that is of greatest value or most suit- 

 able for his particular purposes. The next problem is to obtain 

 a continuation of the desirable qualities generation after genera- 

 tion. The Blue Andalusian fowl is a bird that has won prizes 

 at poultry shows and has some desirable qualities, but breeders 



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Fig. 218. Color inheritance in the Blue Andalusian fowl 



When good specimens of this variety are mated, their offspring produce on the aver- 

 age only so per cent of good Andalusian Blues: the rest are about evenlv divided be- 

 tween white chickens and black chickens. The Blue Andalusian is a hybrid; the only 

 way to get 100 per cent of birds of this kind is to mate a white and a black parent. 



(From Jewetfs "The Next Generation') 



have been unable to get this variety in a pure breed. If we 

 could cut up a Blue Andalusian hen into a hundred or a dozen 

 pieces, as the plant breeder does with some of his prize speci- 

 mens, and then get each piece to grow into a complete hen, we 

 might make some progress in fixing this variety. But this 

 method of propagation is not usable with animals. Each gen- 

 eration has to reproduce by means of eggs and sperms, and that 

 means the danger that hybrids will split up (see Fig. 218). 



Another side of this problem is illustrated by the common 

 mule. This animal is a hybrid also— between the male of the 

 ass and the female of the horse. The mule differs from both 



