MEN DELI SM IN DOMESTIC ANIMALS 471 



be disposed of. As the type becomes well established and there is a wide 

 field of choice among the grays the selection should be further refined by 

 disposing of both parents of any foal of a color other than gray. By this 

 method it should be a simple matter to establish a gray breed of draft 

 horses which would not only breed true to color among themselves, but 

 would also give only gray foals when mated to bay, brown, black, or 

 chestnut horses. 



Mendelism in cattle. The state of knowledge of the inheritance of 

 coat color in cattle is even less satisfactory than that in horses, but there 

 are some results from experimental investigations which have firmly 

 grounded our knowledge of certain points of it. 



White is a natural starting point in the discussion of Mendelian 

 inheritance of coat color in cattle, but it proves to be by no means capable 

 of simple treatment. The difficulty of dealing with white in cattle appears 

 to be due to the variety of whites of different genotypes which are met 

 with. Thus the white of Shorthorn cattle is apparently never a true 

 white, for the eyelashes, face bristles, and particularly the ears always 

 bear some red hairs, although often so few that they are ordinarily over- 

 looked by breeders. This type of pigmentation is not an extreme con- 

 dition of red and white blotching which is often met with in Shorthorn 

 cattle, but it is entirely independent of spotting. This is indicated by 

 the clean cut segregation which this type of coloration exhibits. 

 Lloyd-Jones and Evvard present data which favors the explanation that 

 white with colored extremities depends on a recessive extension factor, e. 

 Another type of white met with in modern breeds appears to be merely 

 an extreme condition of spotting. Such whites are not uncommon . 

 among Ayrshire and Holstein-Fresian cattle, but they are undoubtedly 

 genetically different from whites with colored extremities. The wild 

 white Park cattle of Britain and the white feral herds mentioned by 

 Darwin always have colored ears, but it is doubtful whether they are 

 genetically identical with the white Shorthorn. They apparently 

 produce colored calves at times in spite of the fact that such calves are . 

 never retained in the breeding herds. It is known that some of these 

 white herds were of mixed origin, and that some of them are creamy 

 white rather than pure white. Accordingly it is not impossible that the 

 colored calves which are produced by wild Park cattle are the result of 

 recombinations of complementary factors rather than of recessive 

 segregation. The problem of white in cattle is far from a complete 

 solution. 



Red in cattle varies from a very dark red to light yellowish red. In 

 the early days of the Shorthorn breed all these shades were represented 

 but now the very dark reds and the yellowish reds are looked upon with 

 disfavor. There is a little evidence of sharp segregation between some 



