Wright: Color Inheritance in Mammals 



143 



situation in rodents, but of lesser im- 

 portance than the difference between 

 the stripes. 



FACTORS OF REGIONAL DIFFERENTIATION 



In cats, there is a feature which finds 

 no ]3arallel in the rodents mentioned 

 above. In the latter cases, the difference 

 between back and belly in the activities 

 of enzymes I and II, was supposed to 

 hold for all individuals and to be merely 

 revealed more or less clearly in the 

 different color varieties. In cats, we 

 have actual variations in the localization 

 of the patterns. According to Whiting, 

 the three types of tabby, finely lined, 

 striped, and blotched, segregate sharply 

 in crosses and are probably inherited as 

 a series of three allelomorphs in which 

 the highest dominant is the lined pat- 

 tern, while the blotched pattern is the 

 lowest recessive. Although the stripes 

 differ in the activity of both enzymes 

 I and II we cannot compare this series 

 of factors with the combined factors 

 of classes lb and 2a3. They do not 

 determine an ascending or descending 

 sequence in activity of enzymes I and 

 II, but instead a sequence of types of 

 regional differentiation. Both the dark 

 and light stripes are wide in the blotched 

 tabby, relatively narrow in the tiger 

 tabbv, and reduced to mere lines in the 



lined tabby. The fact that variations 

 of both classes 1 and 2 are involved 

 suggests that the dark strips come to 

 differ from the light ones at some 

 critical period in development by a 

 general metabolic difference which ef- 

 fects the activities of both enzymes, 

 rather than by a specific chemical dif- 

 ference. This was the view adopted to 

 account for the difference between back 

 and belly in the rodents and the differ- 

 ences between males and females in 

 tricolor guinea-pigs. On this view, the 

 Mendelian factors for the different types 

 of striping determine short, mediimi, or 

 long waves during the development of 

 the epidemiis in some general metabolic 

 condition at the critical period in de- 

 velopment for determination of color. 



No other unit Mendelion factors have 

 been noted in mammals which deter- 

 mine a type of regional differentiation 

 but the existence of hereditary factors of 

 this kind was noted in piebald guinea 

 pigs and in cattle. In the latter especi- 

 ally, the different types of pattern which 

 have become fixed in the white-faced 

 Herefords, the white-belted Dutch cattle 

 and the irregular Hoi steins, with a 

 given quantitative grade of piebald, is 

 especially noteworthy. vSuch factors, 

 which determine a type of regional dif- 

 ferentiation, must be put in a new cIpss. 



Table of Factor Comblxations 



V — converts any color into solid white with or without reduction of cn'cs to blue, 

 s — adds piebald white pattern to any color variety. 



i — reduces all black in above patterns to maltese, all orange to cream and cream nearly or 

 quite to white. 



