s 
Research Bulletin No. 2 
THE THEORY OF MULTIPLE FACTORS AFFECTING A SINGLE 
CHARACTER COMPLEX. 
Bateson and later other writers have shown that development 
of qualitative characters may depend upon the interaction of 
two or more gametic factors that are transmitted independently. 
When one of these essential factors is absent from the zygote the 
visible character does not develop. Thus color in the sweet pea, 
in stocks, in snapdragons, in primulas, in beans, and in the hair 
of various animals does not develop unless a basic factor, gen- 
erally known as the color factor C, is present in addition to the 
color determiner which fixes the shade of the color. When either 
the color factor or the specific determiner is absent, color does 
not develop. 
In two papers published in 1908 and 1909. Xilsson-Ehle 
showed that certain colors in wheat and in oats are determined 
not by single gametic factors but by several, the presence of any 
one of which serves to determine the color. In other words, 
these gametic factors, altho affecting the same zygotic character, 
are not allelomorphic to each other, but to their own absence. 
Xilsson-Ehle in 1908 showed how such facts gave a foundation 
for a theory interpreting the inheritance of quantitative charac- 
ters, altho no experimental data were submitted to support the 
hypothesis. 
A little later, East, in ignorance of Xilsson-Ehle's 1908 paper.* 
submitted a similar case of color inheritance in maize, and de- 
veloped a similar theory. 
Fortunately this type of inheritance was discovered in charac- 
ters showing dominance, otherwise its proof would have been very 
difficult. We will describe these cases first, and afterwards show 
their bearing on the so-called "blending" inheritance character- 
istic of quantitative characters. 
Xilsson-Ehle (1909) crossed together many varieties of oats 
differing in glume color. The results from all but one of these 
crosses were quite simple. Presence of color dominated absence. 
Where the parents differed in one character pair, such as black 
(B) and absence of black (b), the ratio in F 2 was 3: 1. Where 
the parents differed in two allelomorphic pairs, black (B) and 
absence of black (b), and gray (G) and absence of gTRj(g), the 
ratio in F 2 was 12 black : 3 gray : 1 white, because the classes 
BG and Bg could not be distinguished. So far there were no 
* East learned of Nilsson-Ehle's second paper, which does not give the 
full development of the quantitative-inheritance theory, after the first 
draft of his own paper was written, but Nilsson-Ehle deserves full credit 
for the theory that is based upon his beautiful results on qualitative 
characters. 
