No. 588] INHERITANCE OF SPOTTING IN MICE 



733 



which obeys the ordinary laws of mendelian inheritance, 

 we should expect that black-eyed whites would be obtained 

 of two genetic types, homozygous and heterozygous. If 

 now black-eyed whites were mated together at random, 

 the matings should be either (1) DD X DD, (2) DD X DR 

 or (3) DR X DR. In the case of (1) and (2) only black- 

 eyed white young should be produced, while type (3) 

 should give approximately 3 black-eyed whites to one pie- 

 bald. Random matings would therefore produce a ratio 

 of black-eyed whites to piebalds considerably in excess 

 of 3:1. 



If, on the other hand, the DD form of black-eyed white 

 mice behaves in a fashion similar to the homozygous yel- 

 low mice, failing to develop, we should expect a ratio of 2 

 black-eyed whites to one piebald young, no matter what 

 the origin of the black-eyed white parents might be, when- 

 ever two black-eyed whites are bred together. 



The results are as follows : 



Black-Eyed White X Black-Eyed White 



Observed ^57 39 



Expected 2:1 ratio 64 32 



When one realizes that the ratio in one case should be 

 considerably higher than 3 : 1, it seems that the results in- 

 dicate a 2 : 1 ratio and the heterozygous nature of black- 

 eyed whites. 



To further test this hypothesis individual tests of 

 twenty-one black-eyed whites coming from black-eyed 

 white parents were made by crossing with piebald 

 animals. If the DD combination is possible, approx- 

 imately seven of the twenty-one tested should be of that 

 constitution. All of them, however, proved to be hetero- 

 zygous. While the numbers should be supplemented by 

 further tests, they are certainly sufficient to serve as a 

 basis for a tentative conclusion that black-eyed white 

 mice are always heterozygous. 



