298 The Genetics of the Dutch Rabbit — A Reply 



back-cross. An hypothesis which works only part of the time cannot be 

 said to work well. 



Why resort to an hypothesis so complicated when a much simpler 

 one will work better ? Punnett's reasons apparently are two, (1) a distrust 

 of explanations involving multiple allelomorphs *and (2) a dislike for the 

 idea of "modification" as implying impurity of the gametes. Now 

 multiple allelomorphism, under whatever name one chooses to discuss 

 it, is no longer an hypothesis but a well-established fact. Even in 

 rabbits we have two other undoubted «ases, one being the albino series 

 of three allelomorphs (Polish, Himalayan, and coloured), the other the 

 agouti series, likewise of three allelomorphs (grey, black-and-tan, and 

 non-agouti). In guinea-pigs there are four allelomorphs in the albino 

 series (Wright), and three in the extension series (Ibsen). In Drosophila 

 there are eight or more allelomorphs in the white-eye series (Morgan), 

 and we have conclusive proof that the linkage relations with other 

 factors are the same throughout the series showing that all occupy the 

 same " genetic locus." If one chooses to regard a series of allelomorphs 

 as constructed on one and the same genetic basis, with additions or 

 subtractions in individual cases, there can be no valid objection to such 

 a view. Thus Himalayan albinism may be regarded as Polish albinism 

 plus a darkening factor inseparably coupled with it, if one prefers that 

 form of description, but the fact is not altered thereby that in crosses 

 the two things behave as ordinary allelomorphs. So, I maintain, it is 

 with different types of Dutch marking in rabbits. I have identified 

 three such types. Punnett has identified positively one of the same 

 types (White) and tentatively recognizes two other types different from 

 any of mine. He seems to regard my two other types as dubious 

 because they are not the same as his. My experience leads me to be 

 more charitable. I am ready to admit the probable existence of five 

 types of Dutch and that all will probably be found to be allelomorphs. 

 I have even found that a very different type of white spotting which 

 occurs in rabbits, viz. English, behaves as an apparent allelomorph of 

 White Dutch. It may, however, only be very closely linked with Dutch, 

 for it seems remarkable that two genes so manifestly different in their 

 physiological properties should be variants of a single genetic locus. 

 But in any case it is not to be inferred that w^hite spotting in mammals 

 generally consists of allelomorphs of one genetic locus. For Little, 

 Detlefsen and Dunn have independently shown that piebald spotting in 

 mice is genetically distinct from black-eyed-white spotting, the two 

 genes manifesting no linkage (Dunn). 



