100 PROCEEDINGS OP THE AMERICAN ACADEMY. 



4D + 1DR+ 4DDR4-4DR+2DRR4- IR- 



Of the 16 individuals, 9 (or tliose of the first three classes just enumer- 

 ated) do not have albinism recessive; G (or the next two classes) do have 

 that character recessive, vphile the 16th animal is a pure recessive. 



Case II. 



Here the heterozygote is D-R, and the homozygote is DR. The result 

 is the same as in Case I, save that there is a slightly different proportion 

 of certain of the pigmented classes, as may be seen from the following : 



D + R = gametes of heterozygote, 



DR + DR = " " homozygote, 



2D-DR + 2DR-R = offspring, or generation Fj. 



The possible unions among the animals of generation Fj are : 



a. h. 



D + DR DR + R 



D + PR DR+ R 



D + 2DDR + DR DR + 2DR R + R 



c. 

 D+ DR 

 DR + R 



2(DDR + DR + D-R + DR R) 

 Total of F, : 



ID + 4DR + 4D-DR + 2DR + 4DRR + IR. 



The writer has not been able fully to test experimentally the relations 

 here worked out, to see if they actually occur under proper crossing. In 

 one instance, however, a chocolate-white male, a pure DR, was bred to a 

 gray heterozygote whose parents were a house mouse and an albino. 

 This mating is therefore of the sort explained under Case II, above. 

 Two litters were obtained from this pair, the one of 5, the other of 6 

 young. All these 11 young were gray. The individuals of the second 

 litter were allowed to grow up and breed together, in order that they 

 might show, if possible, what result would come of their random mating. 

 When about five months old these six hi-terozygotcs produced two lots 

 of young. The first lot consisted of a chocolate and an albino mouse; 



