Wright: Color Inheritance in Mammals 



225 



with certain peculiar relations between 

 the colors. The writer wishes to em- 

 phasize, however, that for the present 

 the chemical terms are used rather for 

 the sake of giving a definite scheme to 

 which genetic facts may be referred 

 than for their own sake. Since the 

 earliest work on color inheritance, 

 many geneticists, notably Cuenot,^ 

 Castle,- and Little,^ have tried to give 

 a physiological interpretation to their 

 results. The hypothesis advanced here 

 is based to some extent on their con- 

 clusions with modifications intended to 

 bring under one point of view certain 

 curious new facts. 



COLOR IN MAMMALS 



Melanin pigment is found in the skin, 

 fur and eyes of mammals. The present 

 paper will deal largely with the gross 

 effects as our knowledge of the ultimate 

 differences of the colors is still very un- 

 satisfactory. Only mammals are dealt 

 with, as in other classes on which genetic 

 work has been done the pigment colors 

 are largely masked by structural effects 



The most highly pigmented condition 

 is found in the color black. The pig- 

 ment granules in this case are not 

 really black but a very dark sepia brown. 

 White in mammals seems always to be 

 a structural color found in the absence 

 of all pigment. There are two dis- 

 tinct series by which black may be 

 reduced toward white. There is first 

 the type of dilution found in brown and 

 tow-colored human hair, or in dilute 

 black guinea-pigs, which reveals the 

 sepia color of the pigment. A very 

 different kind of dilution of black is to 

 be seen in the so-called blue or maltese 

 mammals — blue mice and rabbits, mal- 

 tese cats, etc. The effect is somewhat 

 similar to that in blue roans among 

 horses and cattle and seems to be due 

 to a similar cause on a finer scale. 

 Blue roans have an intermingling of 

 jet black hairs and white hairs while 

 the maltese mammals have dense black 

 pigment masses alternating with color- 

 less spaces within the hair. 



The colors which do not enter into 

 either of these dilution series or their 

 combinations are those which have a 

 distinct orange-yellow tinge such as is 

 seen conspicuously in red human hair, 

 red and yellow cattle, bay, chestnut and 

 dun horses, tan dogs, etc. The most 

 highly pigmented colors of this kind 

 are the so-called reds. The pigment 

 granules appear orange-yellow in such 

 hair, but it does not seem to be settled 

 whether there is an essential chemical 

 difference from sepia-brown granules or 

 merely some structural difference. The 

 appearance of the intense reds varies 

 somewhat in different mammals, but 

 there seems little reason for doubting 

 their essential similarity. Red under- 

 goes different modes of dilution com- 

 parable to those described for black. 

 Reduction to yellow or cream is com- 

 parable to the sepia type of dilution of 

 black, while a more coarsely granular 

 type of dilution comparable to maltese 

 is found in light reds. These light reds 

 are slightly redder in hue than the 

 yellows of similar intensity. The two 

 series may, of course, be combined. 



Finally there are intergrades of vari- 

 ous sorts between the different sepia and 

 yellow series. A coarse-grained mix- 

 ture gives the effect of bay, dun, or 

 sooty yellow depending on the intensity 

 of the colors. A finer type of intergrade 

 seems to be present in the chocolate 

 color of brown mice, rabbits, guinea-pigs 

 and liver-colored dogs. These browns, 

 however, are much closer to the sepias 

 than to the reds and yellows and are 

 not always distinguishable. Genetic 

 evidence sharply distinguishes browns 

 which are due to reduction of black 

 toward white, and browns which are- 

 reductions toward yellow. 



By combining the different kinds of 

 dilution with the different kinds of 

 intergrades between sepia and yellow 

 an almost infinite variety of colors is 

 produced, while the complex patterns in 

 which these colors may be distributed 

 make possible still further diversity in 

 color effect. 



114. 



iCuenot, L. 1903. Arch. Zool. Exp. el Gen. (4), Vol. i. Notes et Revue, p. 33. 



•^Castle, W. E., H. E. Walter, R. C. Mullenix and S. Cobb, 1909. Carn. Inst. Wash. Pub.. 



T.ittle. C. C. 1913. Carn. Inst. Wash. Pub.. 179. 



