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1907.| Transmission of certain Coat Characters in Rats. 99 
The cost of these experiments has been defrayed by a grant from the 
Government Grant Committee of the Royal Society. 
B. THE SYSTEM OF INTERPRETATION OF RESULTS. 
It is possible to adopt at least three ways of representing the allelo- 
morphic pairs, but so far as the results which I have obtained with rats are 
concerned, the predictions are identical in each case. 
One of these “schemes” differs fundamentally from the other two in that it 
regards greyness as not being allelomorphic to blackness, while the other two 
do. There are reasons for believing that greyness and blackness may not 
be allelomorphic. And since this “scheme,” which embodies Bateson and 
Punnett’s “ Presence and Absence” theory, has successfully interpreted other 
results of a diverse nature, it will be adopted in this paper. 
The essential feature in their “scheme” is that the allelomorphic pairs 
consist of a determinant (factor) for the presence, and of one for the absence 
of the character under consideration. On the basis of gametic purity, there- 
fore, any one gamete cannot carry both the positive and negative factor of the 
same character. But it can carry the positive factor for each of two 
characters, such as blackness and greyness. 
This “scheme” predicts accurately the types of rat which result in any 
cross, in so far that types not predicted never appear. In some cases, however, 
predicted types have not appeared, but the evidence is clear that this is due 
only to want of numbers, and that with more litters the missing types will 
duly appear. Indeed, in several instances, when I first tabulated my results, 
a certain type which was predicted was absent, but in most of the cases it has 
since appeared in a later litter. With regard to the expected proportions, the 
prediction is usually approximately, and in some cases exactly, fulfilled. | 
In interpreting my results by means of Bateson and Punnett’s 
“ Presence and Absence” hypothesis, I have conjoined to their conception, 
that of Cuénot, in which he postulates the idea that colour is due to the 
interaction of two bodies, one a ferment and the other a chromogen. This 
idea has received confirmation from Miss Durham’s work. 
Below Ll append the various symbols employed :— 
C = colour producer.* c = absence of colour producer. 
G = grey determiner. = 3 erey determiner. 
B = blackt .. \C L black ‘4 
= self-pattern determiner. We % self-pattern determiner. 
P = piebald-pattern determiner. p= " piebald-pattern determiner. 
* Tn this paper the colour producer is regarded as a ferment. 
+ In this paper the grey and black determiners are regarded as chromogenous bodies 
which develope colour when acted upon by the ferment C. 
