UNIT-CHARACTERS OF CATTLE 133 



spotting has been so fixed by selection that it shows itself (as 

 a white forehead) in crosses with self-colored breeds and even 

 in hybrids with the American bison. 



Yellow spotting on a black background is not very com- 

 mon among cattle, no standard breed with this characteristic 

 being known, but a brindling of yellow and black spots is oc- 

 casionally seen in mongrel animals and no doubt good black- 

 and-yellow spotted animals could be produced, if it were 

 considered sufficiently desirable, or even tri-colors with black- 

 yellow-and-white coats. It is possible that brindling (yellow 

 spotted with black) is a third allelomorph of black and of 

 yellow, as in guinea-pigs. 



A morphological variation of cattle of some economic im- 

 portance is hornlessness. This has occurred among cattle of 

 Scotland and England for several centuries at least and is 

 known also to have occurred among cattle kept on the conti- 

 nent and still earlier to have occurred among cattle of the 

 ancient Egj'ptians. Loss of horns is a completely discon- 

 tinuous variation, dominant in crosses. Heterozygotes may 

 develop mere traces of horns, known as scurs, but never a 

 fully formed horn with bony core. Hornlessness has become 

 an established racial character (homozygous) in the Scotch 

 breeds of black cattle, Aberdeen Angus (Fig. 73) and Gallo- 

 way, also in an English breed of red cattle called Red 

 Polled. Within the last thirty years polled sports have 

 appeared in pure-bred Holstein cattle in the United States 

 and a breed of polled Holsteins is now being established in 

 this country. A breed of polled Herefords was produced in 

 the United States from a three-quarters Hereford, one- 

 quarter short-horn polled calf born in 1889. (Wallace, p. 

 122.) See Figs 68 and 71. Polled cattle are easier to manage 

 and less liable to injure each other than are horned cattle. 

 There can be no doubt that hornlessness had its origin as a 

 unit-character variation dominant in crosses. 



Another morphological character, said to be a Mendelian 

 dominant, occurs in Dexter-Kerry cattle. They have ab- 

 normally short, stumpy legs. (See Figs. 60 and 61.) 



