ALLEN. — THE HEREDITY OF COAT COLOR IN MICE. 139 



The expected result, provided that the gametes retain their purity 

 with respect to pigment characters, is tliat cue-fourth the offspring 

 will be black, and one-fourth golden-agouti, while the remaining one- 

 half will be gray, since they represent unions involving the three different 

 sorts of pigment characters. The actual result was of this nature, for 

 the three classes were present in the two litters obtained in the following 

 numbers of individuals : 2 black, 2 gray, 8 golden-agouti. This, then, 

 has the appearance of a simple case of Mendelian inheritance, wherein 

 two pigment characters (black and golden-agouti) are produced in 

 separate gametes equally numerous. 



A further test of this hypothesis was made by back-crossing one of 

 the gray (black X golden-agouti) mice with a golden-agouti female. 

 If the gray mouse produces gametes whose pigment characters have 

 kept their integrity, the two sorts of unions possible would give equal 

 numbers of gray and of golden-agouti young, thus : 



bl. -|- gold-ag. = gametes of gray male, 



gold.-ag. -\- gold.-ag. = " gold.-ag. female, 



2 gray + 2 gold.-ag. = offspring. 



If, however, as in certain cases previously described, it be assumed 

 that one-half the unions only are of this sort, while in the other half 

 the gametes of the golden-agouti parent undergo resolution, the result in 

 this latter case would be : 



bl. -|- yell.-ch. = gametes of gray male, 



ch. + yell.-ch. = " gold.-ag. female, 



1 bl.-ch. + 2 gold.-ag. -f- 1 gr. = offspring. 



The total result would be four (50 per cent) of golden-agouti young, 

 three (or 37i per cent) of gray young, and one (or 12^ per cent) black, 

 if the union of black with yellow results in black. These three classes of 

 colors were all present in the single litter obtained, but the proportions 

 were : one golden-agouti, three gray, one black. This experiment is not 

 conclusive, therefore, but indicates that in some cases the gametes may 

 retain their pigment characters intact, whereas in other cases these 

 characters may undergo resolution. On the other hand, it is conceivable 

 that the gray animal represents merely the coexistence of the three 

 characters in the germ-cells as well as in the soma, and that it is a matter 

 of chance whether at gamete formation the three pigment elements be- 

 come variously segregated or remain together in one gamete. Such 



