ALLEN. — THE HEREDITY OF COAT COLOR IN MIC£. 145 



One of the three gray young from the cross of the gray heterozygote 

 and the chocolate female was back-crossed with the same chocolate 

 mouse, its mother. The single litter obtained consisted of 2 gray, 1 black, 

 and 1 chocolate offspring, a fact which probably indicates that the gray 

 animal produced a certain number of gametes with the black character, 

 and others with the chocolate chaiacter. The number of young obtained 

 is, however, too small to allow of generalization. 



This same gray male was also mated with an albino female which 

 transmitted the black pigment character. If chocolate always goes with 

 black, the combinations of pigment characters represented by this mating 

 are probably as follows : 



bl.-ch. -f yell.-ch. = gametes of gray parent, 

 bl.-ch. + bl.-ch. = gametes of albino parent, 

 2 black -f 2 gray = offspring. 



The observed result was 3 black, and 4 gray mice, so that, although 

 the totals obtained are small, it seems probable that the gray character 

 did undergo resolution in the manner suggested. 



Evidence has been adduced from the experiments cited by Bateson and 

 from those performed by the writer to show that the black coat character 

 may be a simple dominant over chocolate. The relation of the chocolate 

 character to golden-agouti may next be considered. 



4. The golden-agouti type. This is the type of mouse which Bateson 

 describes as possessing the chocolate and the yellow pigments, but not the 

 black. It therefore has a dingy or tawny appearance. Microscopical 

 examination of the hairs of certain mice bred by the writer confirms this 

 description. 



These mice occurred in small proportion among the young of gray 

 heterozygotes, themselves the offspring of black-white and albino mice, 

 and hence are evidence that a resolution of color characters took place in 

 the gametes of their gray parents. Since the golden-agouti contains but 

 the two pigments, yellow and chocolate, the utmost number of varieties 

 obtainable by interbreeding two animals of this sort is manifestly three, 

 assuming that both pigment characters undergo resolution in the same 

 manner. These would be, a pure yellow, a pure chocolate, and the com- 

 bination of the two, or golden-agouti. In the writer's experiments, only 

 the last two types have appeared. No pure yellow mouse has been 

 obtained among all the various crosses, which have produced hundreds of 

 offspring. This fact may point to some physiological peculiarity in case 

 of the writer's stock, by reason of which the yellow pigment character 



VOL. XL. — 10 



