448 H. J. MULLER 
B. Its reactions with the W series of allelomorphs 
The nature of the mutation was determined by testing the 
ivory males. When mated to white females these males pro- 
duced daughters that were nearly white in color, thus indicating 
the gene to be an allelomorph of white. It has been found that 
females heterozygous for ivory and for any one of the following 
allelomorphs of white are intermediate in color between homo- 
zygous ivory females and females homozygous for the other 
TABLE 2 
Sa ene eS lad EP ORBOVER at ee 
cae wi e, So 7 ios io EN TOTAL 
Shearer Ss, Ww We, | S, Wr e 
4880 Te 44 0 0 1 0 0 117 
4881 64 7A 0 0 1 0 0 139 
4884. Tal 53 2 0 3 0 0 129 
4885 57 69 3 2 Pe 3 0) 136 
4886 48 41 3 1 2, 3 0 98 
4887 46 30 0 2 5 2 0 85 
Mota... i. 358 308 Go aes Zam ta 0 704 
666 13 25 
IPErCei tage can eee 18 3.6 
color: Blood, cherry, eosin, tinge, buff, écru. (Coral has not 
been crossed to ivory.) The color of the heterozygous ivories 
is not only intermediate, but varies in proportion to the inten- 
sities of color produced by the other allelomorph when the latter 
is homozygous; thus, for example, blood-ivory is darker than 
eosin-ivory, pure blood being darker than pure eosin. 
It has been observed by Muller that the ivory males are on 
the average slightly lighter than the homozygous ivory females. 
C. Locus of ivory 
An ivory male from 4711 was mated to scute echinus females, 
and the daughters produced the sons shown in table 2. 
