148 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



Both animals of this pair, numbers 451 and 477, had albinism reces- 

 sive, that character having been handed on in this condition throuf;'h four 

 generations in case of the J" 451. For in the first litter obtained from 

 them there were 3 albino, 2 chocolate, and 1 golden-agouti young. It 

 is ditheult to see how the female of this pair could have inherited a 

 recessive chocolate character, though the male might conceivably have 

 done so, through the chocolate grandparent. 



If chocolate be recessive toward golden-agouti, a cross between 

 " pure " animals of these two colors should result in offspring of the 

 latter pigment type only. Only two crosses have thus far been made 

 by the writer between these two varieties. In the one, a golden-agouti 

 male, 245, was bred to a chocolate female, 244, and in three litters there 

 resulted 10 chocolate to 7 golden-agouti offspring. In the second case, 

 a golden-agouti female, 409, was paired with an albino of chocolate 

 parentage, known by tests to have the chocolate pigment-character only. 

 Two young, a chocolate and a golden-agouti, resulted, so that these two 

 pairs of mice are comparable with respect to the pigment characters they 

 transmit. If, then, the golden-agouti parent of each pair can have jdos- 

 sessed chocolate in a recessive condition, the approximate equality of 

 the two sorts of young among the offspring is readily explicable on 

 Mendelian principles. The ancestry of the two golden-agoutis is as 

 follows : 



^ bl.-wh. „ , ^ bl.-wh. o 1 * u n V, 

 1-21 ° ' 1 • 2 1 ° ' ° ° house mouse. 



(? bl. 9 gr. c? gr. 



92 91,93 82 



9 gr. c? gr. g , (? bl.-wh. r> ^u 

 86 51 ^ ^^- 1 ■ 2 b. ^ '^^• 



S gold.-ag. 245 ^ ch.-wh. 328 9 wh. 192 ^ bl. 92 9 gr. 91 



S gr. 407 



9 ch. 276 



9 gold.-ag. 469 



If the golden-agouti ^ 245 contains the chocolate character recessive, 

 it must have come from the black parent through resolution. The gray 



