ALLEN. — TUE HEREDITY OF COAT COLOR IN MICE, 131 



The black heterozygotes of this same (F2) geueratiou, when interbred, 

 produced only black-whites (4), blacks (7), and albinos (6). Thus the 

 black failed to undergo further resolution, and it contained no other pig- 

 ment in a recessive condition. This result is like that recorded by von 

 Guaita, whose black mice, when interbred, produced no other color type 

 than black. 



Wiien, liowever, gray heterozygotes were bred to black heterozygotes, 

 both of the Fi generation, the result was similar to that given by the gray 

 animals bred inter se. For from this mating there resulted: gray (14), 

 gray-white (5), black (5j, black-white (2), chocolate (4j, golden-agouti 

 (4), pied golden-agouti (1), albinos (5). 



These results show that gray with its three pigment elements is more 

 readily resolvable than is the black, which consists of but two pigments. 

 As will be shown presently, it is sometimes possible to obtain chocolate 

 mice from black parents, hence it might have been expected that individ- 

 uals of this color should occur among the offspring of the gray and black 

 heterozygotes. But the presence of golden-agouti among these offspring 

 seems plainly due to the introduction of the third or yellow pigment char- 

 acter through the gray parent. Moreover, when resolution does take 

 place, the yellow element is the first to disaj^pear, so that black individuals 

 are next in point of numbers to the gray ones, and are nearly twice as 

 numerous as either the golden-agouti or the chocolate mice. Leaving the 

 albino young out of consideration, it is seen that in the cross of gray 

 heterozygotes, resolution of the pigments took place with such frequency 

 as to produce 12 individuals lacking one or two of the three pigments, as 

 against 43 which possessed all the pigments and so were gray. In the 

 cross of gray with black mice of the same (F^) generation, 15 showed 

 resolution of color, as against 19 which were gray. It is difficult to draw 

 any definite conclusions as to the proportions of germ cells in which the 

 pigment characters undei'go resolution. For it is hardly probable that all 

 the gray individuals result from the union of gametes each of which has 

 the gray character, since this color might be produced by the union of 

 any two gametes which together contained the three elements ; thus gray 

 X black, gray X chocolate, gray X yellow, as well as black-chocolate X 

 yellow, or yellow-chocolate X black might result in the production of 

 gray individuals. The writer has been unable to obtain mice with the 

 yellow pigment alone by this process of segregation, but this negative 

 result is not surprising when we recall that in the experiments of vou 

 Guaita (:00) neither chocolate nor golden-agouti types wei'e produced, 

 though these have appeared repeatedly in the writer's experiments. 



