166 Inheritance of Coat Colour in Mice 



There were no chocolates, no cinnamon agoutis, no pink-eyed agoutis 

 of either sort, and no blue lilacs. 



I have tried other raatings of various sorts but the numbers yielded 

 are too small to be worth quoting. 



Yellow Mice. 



The genetic behaviour of yellow mice differs in various particulars 

 from that of other mice ; and there is at present no very satisfactory 

 explanation possible to account for this. 



Hagedoorn(l) is the only one among many breeders of yellow mice 

 whose experiences are not in accordance with my own. But from his 

 account of his experiments, it is clear that he was using a different 

 type of yellow mouse from that employed by the rest of us. 



The type, which I and other breeders have used, must be regarded 

 as a heterozygous dominant. For it never breeds true, no homo- 

 zygous form has yet been obtained; and when mated with mice of 

 other colours than yellow, some of the offspring are always yellow. 

 Hagedoorn's mouse was a recessive and did breed true. His experi- 

 ments are of interest as showing that another type of yellow mouse 

 exists, but his results need not be considered further here. 



I made 185- matings in all between yellows bred in every kind of 

 way, but every one of these yellows proved to be heterozygous. 



As a result of 127 matings between yellows I obtained 448 yellows 

 and 232 other colours. I purposely excluded from the list all matings 

 from which sables and albinos were obtained, so as to count only the 

 pure yellow forms. Albinos can carry the yellow determiner, and the 

 sable mouse, which is perhaps only a variant of the yellow, presents so 

 many peculiarities as I shall show later on that for the present purpose 

 I preferred to exclude it. 



As a result of 104 matings between yellows and other colours I 

 have obtained 297 yellows and 336 other colours. 



The problem created by the absence of pure yellows has been dis- 

 cussed by Cu^not(2), Castle (5), Wilson, Morgan and others. There are 

 two possibilities: (1) that in fertilization the zygotes, yellow x yellow, are 

 never formed; (2) that these zygotes are formed but perish. If they 

 are not formed we should expect the ratio of yellow to non-yellow to 

 approximate in .Pg to 3 : 1, because the number of spermatozoa is 

 indefinitely large; if on the other hand such zygotes are formed and 

 perish, the F.^. ratio should be 2 : 1. 



