408 



THE AMERICAN NATURALIST 



[Vol. LIV 



ing from 12 per cent, to 85 per cent, of white. Other in- 

 vestigators have recorded piebalds whiter than this 2 and 

 one or two of my crosses indicate that piebalds may ex- 

 hibit as much as 60 per cent, or 65 per cent, white, al- 

 though such animals have been extremely rare in these 

 experiments. 



Genetically these two types of spotting are distinct, 

 and each is due to a gene distinct from and independent 

 of the other. When black-eyed whites are crossed with 

 piebalds equal numbers of black-eyed whites and piebalds 

 result. When black-eyed whites are bred inter se, black- 

 eyed whites and piebalds result in the ratio of 2:1. The 

 black-eyed white condition is therefore due to a gene 

 (symbol W) acting with the gene for piebald (symbol s). 

 Black-eyed whites are heterozygous for the gene W and 

 are homozygous for s. Genetically they are Wwss. Pie- 

 balds may be represented by the formula wwss, where w 

 stands merely for ' ' not-black-eyed white." These two 

 genes, as is known from previous data (Little, 1915; 

 Dunn, 1920), are neither allelomorphic nor linked, but 

 entirely independent. 



As additional evidence of the distinctness of these 

 types and to illustrate the comparative ranges as re- 

 gards amount of white spotting on the dorsal surface, 

 the data from a number of crosses between black-eyed 

 whites and piebalds are presented in Table II, Cross 1, 

 and Fig. 1 solid line. All mice in this as in other dis- 

 tributions to be discussed were graded by estimating 

 the amount of white in the coat. The two surfaces, dor- 

 sal and ventral, were graded separately, the total of each 

 surface being regarded as 100. The percentage of dorsal 

 white was expressed as the numerator and the per- 

 centage of ventral white as the denominator of a fraction. 

 Thus a mouse entirely white dorsally and ventrally (ex- 

 cept for pigment in the eyes) was graded as 100/100; 

 while one with only a small patch of white ventrally was 



2 For instance, the race of pure Japanese piebalds described by Little 

 <1917) which varied from 100 per cent, to 64 per cent, white dorsally and 



