WHITE SPOTTING IN MICE 



475 



1 wwss— piebald 

 16 



The visible distribution should consist of approximately 

 2 black-eyed whites, 7 spotted, and 3 self. The experi- 

 mental numbers for this cross (Table I, Cross 4) in the 

 present study are 16 black-eyed whites, 27 "spotted," 3 

 and 18 self s. Among the spotted forms is included a new 

 genotypic class consisting of mice which are heterozygous 

 for W but pure for self. Little called this genotype 

 "dark spotted," but since somatically it is no darker than 

 other spotted types I shall refer to it arbitrarily as Type 

 "C." Some of the spotted mice from the above cross (4) 

 were tested by crossing them with piebalds. If the mouse 

 tested were piebald, it should produce only spotted (pic- 

 bald) mice; if it were Type "A" it should produce black- 

 eyed whites, spotted and selfs ; while if it were Type "C" 

 it should produce only spotted (Type "A") and self. 

 Out of a number of mice so tested only seven proved to 

 be Type "C" and the only evidence available on the ap- 

 pearance of Type "C" mice is from the appearance of 

 these tested animals. Five were less than 5 per cent, 

 white dorsally ; one was 7 per cent, white and one was 8 

 per cent. The white spotting in all of them was confined 

 to the head, either as a spot on the nose or between the 

 eyes ("blaze"). It is to be regretted that no animals 

 from this cross with less than 12 per cent, of ventral 

 white were tested, since it seems probable from the ex- 

 cess of selfs recorded that some mice graded as self and 

 were really Type "C." The same excess of selfs was 

 noted in a larger amount of data on this cross reported 

 by Little. Its significance is probably the same, that is, 

 it is due to the production of an extremely small amount 

 of spotting by the genetic Types "A" and "O. 



85 offspring (Table II, Cross (!). of which were spotted 

 and 42 were self (expected 42.5 of each). The spotted 



