Wright: Color Inheritance in Mammals 



89 



from black and liver by a recessive unit 

 factor. Little^ obtained satisfactory fig- 

 ures demonstrating this point in 

 Pointers, and Barrows and Phillips^ 

 confirm it in Cocker Spaniels. The 

 presence of this factor difference be- 

 tween red Pekinese and black Pomera- 

 nians has just been noted. 



This, however, leaves uncertain the 

 genetic relations of the various kinds 

 of mixtures of black and yellow. The 

 common color of Collies is a sort of 

 sooty yellow; in Great Danes, Bull 

 Terriers and other breeds there is a 

 brindle pattern and many breeds are 

 characterized by the black-and-tan pat- 

 tern in which the feet, belly, and parts 

 of the head are tan or yellow, the rest 

 of the coat being black. A similar 

 pattern is found among the wild 

 canidae. 



THE TRICOLOR PATTERN 



In many breeds both the piebald and 

 the black-and-tan pattern are present 

 together. The result is a tricolor. The 

 mode of inheritance of tricolor is of 

 special interest because it was the 

 character in Bassett hounds, which was 

 chosen by Galton^ in his pioneer 

 investigations of the laws of heredity. 

 The tricolor Bassett hoimds continually 

 throw bicolor lemon and white, and vice 

 versa. 



Galton demonstrated heredity in this 

 case, and showed that his law of an- 

 cestral heredity would fit the results 

 satisfactorily. This law claims only to 

 describe the average results in a dog 

 population mated at random as regards 

 color and is not intended to apply to 

 particular cases. As Castle^ has pointed 

 out, no simple Mendelian ratios are 

 to be expected in this case, in which 

 the occurrence of bicolors depends on 

 the arrangement of two independent, 

 fluctuating patterns. Castle compared 

 the case with that of tricolor guinea- 

 pigs, which result from the combination 

 of the piebald and tortoise shell pat- 



terns, with genetic results as confusing 

 to follow as the Bassett hounds. 

 Hagedoorn^ pointed out that the black- 

 and-tan pattern in dogs is a more 

 symmetrical pattern than the tortoise 

 of guinea-pigs, but in the main accepted 

 Castle's view. Ibsen^" pointed out 

 that Bassetts have a reduced type of 

 the black-and-tan pattern, like that 

 of Airedales, in which there is only a 

 blanket of black on the back, leaving 

 the head yellow. As the white of the 

 piebald pattern affects the back before 

 the head, lemon and white is more apt 

 to be produced than black- and white 

 on reduction in the number of colored 

 spots. It is clear that the mode of in- 

 heritance of tricolor can best be solved 

 by studying the heredity of the pie- 

 bald and the black-and-tan patterns 

 separately. 



Barrows and Phillips ^^ identify the 

 pattern of black-and-tans with that 

 of liver-and-tans, and of red-and-lemons. 

 They state that a recessive factor is 

 responsible for the production of these 

 "bicolors" from blacks, livers, and reds 

 respectively. A priori the indentifica- 

 tion of the patterns of black-and-tans 

 and liver-and-tans, seems probable 

 enough, but red-and-tan seems to in- 

 volve a different kind of factor. The 

 first two involve variations in extension 

 of a dark color, and therefore involve 

 factors of class 2 while the last is a 

 pattern of intensity which would seem 

 to fall in class 1. 



It has been noted that in the rodents 

 and in cats there is a tendency for the 

 processes of producing color in general 

 (involving enzyme 1) and of producing 

 black (involving enzyme II) to be weak 

 in the same parts of the coat. Thus the 

 patterns of intensity of color (particu- 

 larly of yellow) and of extension of 

 black, tend to be similar, although 

 brought out by wholly independent 

 Mendelian factors . For example yellow- 

 bellied gray mice differ from solid grays 

 for a wholly different reason from that 



6 Little, C. C, 1914. Journal Heredity, 5:244-248. 

 « Barrows, W. M. and J. N. Phillips. Loc. cit. 

 7 Galton, F., 1897. Proc. Roy. Soc. Lond., 61. 

 sCastle, W. E., 1912. Amer. Nat., 46:437-440. 

 sHagedoorn, A., 1912. Amer. Nat., 46:682. 

 "Ibsen, H. L., 1916. Genetics, 1:367-376. 

 "Barrows, W. E. and J. N. Phillips. Loc. cit. 



