No. 540] INHERITANCE OF COLOR IN CATTLE 733 



25 per cent, pure Shorthorn, 50 per cent, blends and 25 

 per cent, pure Angus in the F 2 generation. If all the in- 

 dependent units moved with absolute synchronism this 

 would be expected, but they are genetically independent 

 and the laws of chance demand that the greater the num- 

 ber of units the more intricate becomes the task of ex- 

 tracting an animal with the combination of a great num- 

 ber of arbitrarily selected traits such as compose any of 

 the pure breeds of domestic animals. 



Barrington and Pearson in referring to the blue-gray 

 hybrid and white Shorthorn cross give evidence showing 

 that sometimes blue-gray, sometimes "grizzled" and 

 sometimes white animals result. 6 Quoting Mr. Hodgson, 

 they say: "This cross gives white cattle which are not, 

 however, to be reckoned as pure white Shorthorns." 7 If 

 all the characters essential to differentiating "pure- 

 bred" Galloway and "pure bred" Shorthorn cattle 

 from each other were reduced to their ultimate 

 inheritable units, the laws of chance having free play, 

 we should expect in F 2 one "pure-bred" Short- 

 horn and one "pure-bred" Angus in 4" individuals — in 

 which n is the number of ultimate units. A conservative 

 estimate would certainly make this number at least a 

 score, but more likely a hundred or a thousand. Taking 

 into consideration the fact that the phases of the units 

 patent in Shorthorn and Angus cattle are not uniformly 

 dominant or recessive, that the same units that distin- 

 guish Shorthorns from cattle in general may not also dis- 

 tinguish Angus from cattle in general, it is obvious that the 

 chance of producing a "pure" animal in from such a 

 combination is very remote. Thus, if the differentiating 

 traits be uniformly dominant or recessive and only ten in 

 number, the chance of securing such a combination would 

 be one in 1,048,576. The close and exceptional fitting of 

 many cases to the simply four-part Mendelian ratio is the 

 only conclusive evidence of the location of the ultimate 

 unit. It is infinitely easier to approximate one of the 



'Ibid., p. 433. 

 7 Ibid., p. 433. 



