156 PROCEEDINGS OF THE AMERICAN ACADEMY. 



gray and sometimes also black offspring, according as the gray character 

 l)resent in the albinos remains unresolved or undergoes resolution. 



The black-pigment character appears to be dominant over the choco- 

 late character, so that a black mouse, or an albino bearing the black 

 character latent, gives only black young when bred to a chocolate indi- 

 vidual. These black heterozygotes bred inter se may produce both black 

 and chocolate offspring, in approximately the ratio, 3:1, or if back- 

 crossed with chocolate mice, the two classes may appear in nearly equal 

 proportions among the young. 



When black mice, or albinos bearing the black character, are bred to 

 golden-agoutis, the three pigments constituting the gray coat are brought 

 together by the union, and gray offspring result. Black young may also 

 occur, in small numbers, indicating either a resolution of the yellow- 

 chocolate character of the golden-agouti, or the segregation of the choco- 

 late character present in either a recessive or a latent condition in the 

 golden-agouti parent. It should, therefore, be possible to obtain chocolate 

 young also from the cross of such a golden-agouti with a black animal 

 having the chocolate character recessive. 



No evidence has been obtained to show that black may be a sim})le 

 dominant over golden-agouti, for gray offspring regularly result from 

 mating pure black with pure golden-agouti mice. P^rom such gray 

 heterozygotes, a second generation was obtained, consisting of black, 

 gray, and golden-agouti young, and indicating, therefore, that the black 

 and the golden-agouti characters kept intact. One of the heterozygotes 

 was back-crossed with the golden-agouti parent and produced the same 

 three coat characters, black, gray, and golden-agouti. The golden-agouti 

 parent, in this case, must have produced some gametes with the chocolate 

 character only, so that black young resulted. (3) The chocolate type, 

 represented by mice having pigment of that color only, breeds true, 

 even if one of the parents contains albinism recessive. Chocolate 

 mice, whether having albinism recessive or not, therefore, contain 

 no other pigment-character. Albinos of two chocolate parents will, 

 on being bred to chocolate mice, produce offspring having only the 

 chocolate-pigment character. 



Chocolate mice, bred to albinos of gray parentage, produce gray 

 young. Black young have resulted, in a few cases, from breeding choco- 

 late mice to albinos of mixed ancestry. This fact probably indicates a 

 segregation of the color characters borne by the albino, in such a manner 

 that the black character is present with chocolate, but without yellow, in 

 some of the gametes, and is dominant over the chocolate character of the 



