386 MENDEL'S LAW AND THE HEREDITY OF ALBINISM. 



IV. PARTIAL ALBINISM A MOSAIC OF DOMINANT AND RECESSIVE 

 CHARACTERS, AND A UNIT IN HEREDITY. 



Darbishire (: 02, : 03) finds that in crosses between a peculiar race of partial albino 

 mice and true albinos, the albinism does not entirely disappear in the offspring, and 

 he thinks that this weighs heavily against the entire Mendelian hypothesis. In reality 

 Darbishire's observations, when rightly interpreted, afford strong evidence in favor 

 of that hypothesis. It may be well, therefore, to examine them with some care. 

 But before doing so one or two earlier observations should be noticed. 



Haacke ('95) crossed spotted blue-[black-]and-white Japanese dancing mice 

 with albino mice, and obtained offspring uniformly gray in color, like the wild house- 

 mouse, or uniformly black. Occasionally, however, one of the gray or black offspring 

 bore a fleck of white on forehead or belly. 



Von Guaita ('98, :00) repeated the experiment, crossing spotted black-and-white 

 Japanese dancing mice with an inbred stock of albinos. He obtained twenty-eight 

 young, all uniformly gray like the house-mouse. These gray mice bred inter se yielded 

 in subsequent generations gray, gray-white, black, black-white, and white offspring. 



Darbishire's experiment consisted in crossing albino mice with a peculiar race 

 of Japanese dancing mice which had pink eyes and were uniformly white except for 

 patches of pale fawn-color on the cheeks, shoulders, and rump. The dancing mice 

 had been tested and found to breed true inter se. From the cross between these 

 partial albinos and true albinos a total of 203 young was obtained, all dark-eyed and 

 with bodies more or less extensively pigmented. As to color, which is recorded 

 for all except the latest litters, the hybrids show the following distribution : 7 yellow : 

 138 gray : 9 black. Of these, seventy-eight gray and six black mice were spotted 

 more or less extensively with white, while the seventy unicolored mice were, all 

 except one, of a lighter color on the belly and tail. In only three out of the entire 

 one hundred and fifty-four for which a full record of the coloration is given, is the 

 pigmentation less extensive than in the pigmented parent. Even in these three the 

 intensity of the pigmentation had been increased by the cross, for the offspring were 

 gray pigmented, whereas the pigmented parent had been merely spotted with light 

 fawn. 



Darbishire's experiment is instructive in a number of ways: 



1. It completely confirms the conclusion based upon the experiments of Crampe 

 ('85), Haacke ('95), von Guaita ('98, :00), Cue"not (:02), and ourselves (Castle and 



