Mendelism 



267 



A few examples of what breeders have accomplished may 

 be of interest. Professor Castle has shown that there is in 

 guinea pigs a factor which restricts black and brown pigment 

 to the eyes, while yellow pigment is unaffected by it. When 

 a brown pig is crossed with a black-eyed yellow one con- 

 taining this factor, some of the offspring receive it in com- 

 bination with the factor for brown and are consequently 

 brown-eyed yellow a new " creation" unknown before Cas- 

 tle's experiments were made. While brown-eyed yellow 



A HERD OF HORNLESS CATTLE 

 Hornlessness may be bred in cattle by proper attention to Mendelian 



laws. 



Courtesy of the U. S. Bureau of Animal Industry. 



guinea pigs may not mean any more to the fancier in dol- 

 lars and cents than do black-eyed yellow ones, nevertheless 

 the experiment demonstrates the possibility of scientific 

 breeding in the production of varieties which do have eco- 

 nomic value. 



The presence of horns on a vicious bull, or a refractory 

 cow, has always constituted a serious menace to the owner's 

 peace of mind, and often such animals have to be dehorned. 

 But the breeder has a better means for dehorning his stock, 

 for lack of horns in cattle is dominant to the horned condi- 

 tion, and by crossing horned cattle with hornless ones of other 



