146 PROCEEDINGS OF THE AMERICAN ACADEMY, 



was unable to assert itself to the same degree as did the black and the 

 chocolate, or j^erhaps the complete resolution never took i)lace.* 



A number of matings were made between golden-agouti mice, and the 

 usual result was offspring all golden-agouti in color. In case of two 

 pairs of golden-agouti mice, however, chocolate young resulted, as well as 

 those of the parents' color. The ancestry of the first of these two pairs is 

 as follows : 



$ bl.-wh. 1 • 2 b. 9 wh. $ bl.-wh. 1 • 2 b. 9 wh. 



$ bl. 92 9 gr. 91, 93 $ gr. 82 9 gr. 81, 86 



$ gold.-ag. 225 9 gold.-ag. 224 



gold.-ag. 295 9 ch. or gold.-ag. ? 



9 gold.-ag. 444 

 The golden-agouti female, 444, was bred back to her father of the 

 same color, 295. The writer is not absolutely certain which of two 

 animals was the mother of the female 444, a chocolate or a golden- 

 agouti, both of which happened to be with the $ 295 at the time. 

 More probably, however, a chocolate mouse was the mother. At all 

 events, on back-crossing the golden-agouti daughter with her father, 3 

 golden-agouti and 2 chocolate young resulted. If both animals in this 

 cross had the chocolate character recessive, this result is readily explica- 

 ble. It is not entirely clear, however, that this was the case. If 

 chocolate be recessive to pure golden-agouti, it is plain that 9 444 is 

 heterozygous with respect to the two characters. It therefore remains 

 to show that her father, 295, was of a similar nature. The parents of 

 $ 295 were both golden-agoutis, the one from two gray parents, the 

 other from a gray and a black parent. The black parent could jjroduce, 

 by resolution of its pigment characters, only the black or the chocolate. 

 Assuming that the latter character only was present in some of the 

 gametes of the black animal, and that one of these united with a gamete 

 from the gray animal that contained both the chocolate and the yellow 



* Bateson, in a letter to Professor Castle, received some time since, suggests 

 that tlie yellow color of certain fancy mice may be due, not to resolution of the 

 wild gray coat, but to crossing with Mus sylvaticus, " which has almost certainly 

 taken place." 



