COLOR INHERITANCE IN MAMMALS 



VI, Cattle — Explanation of Reds, Roans, Whites in Short-horns Long a Matter of 



Dispute — Analysis Shows That Only a Single Pair of Mendelian Factors 



Can Be Involved aside from Minor Variations — Colors in 



General Determined by Combination of Independent 



Sets of Allelomorphs and not by Polygamous 



Factors — Dun the Dilute Form of Black 



Sewall Wright 



Bureau of Animal Industry, Washington, D. C. 



THE first colors in cattle to receive 

 attention from geneticists were 

 the whites, roans and reds of 

 Shorthorns. Barrington and 

 Pearson^ made a study of Shorthorn 

 herdbooks in 1906 with conclusions ad- 



Red 



Red X red 1,710 



Red X roan 1,763 



Red X white 20 



Roan X roan 664 



Roan X white 8 



White X white 4 



4,169 



verse to Mendelian inheritance. Wil- 

 son, ^ however, soon pointed out how 

 closely the general facts fitted with the 

 hypothesis that roan is the heterozygote 

 between red and white. Since then 

 rrany investigations have been made on 

 the question with essentially similar 

 results. There is a general harmony 

 with unit factor inheritance, but also a 

 sir all per cent of well authenticated dis- 

 crepancies with theory, even after allow- 

 ing for the known inaccuracy of herd 

 books. The stmimary by Went worth' 

 given at the bottom of this page illus- 

 trates the case well. The last column 

 gives the expected munber of young 

 from each kind of mating, if mating 

 were wholly random as regards color. 



UNIT, NOT MULTIPLE FACTORS 



Various multiple factor hypotheses 

 have been devise to meet the situation. 

 Laughlin* advanced an hypothesis in- 

 volving four pairs of factors and two 

 physiologically distinct groups of hairs 

 scattered over the body. By this 

 means any particular case that might 



3,780 



47.9% 43.4% 



756 

 8.7% 



8,705 



8.705 



1 Pearson, K. and Barrington, A. 1906. Biom., 4:427. 



2 Wilson, J. 1908. Sci. Proc. Roy. Dub. Soc, 11. 



3 Wentworth, E. N. 1913. Amer. Breed. Mag., 4: 202-208. 

 * LaughUn, H. H. 1912. Amer. Nat. 45:705. 



521 



