302 Is the Fertile Tortoise-Shell Tom Oat a Modified Female? 



is admitted. Furthermore, the breeding behaviour of such fertile tortoise- 

 shell males, can, on the hypothesis of non-disjunction be predicted. When 

 this is done, the prediction coincides with the observed experimental 

 results. The animal should breed like an ordinary yellow male, as the 

 animal reported by Sir Claude Alexander appears to have done. 



On the hypothesis of hormone action, the appearance of a fertile 

 male individual representing a completely transformed female is, in 

 itself, a difficult situation to imagine. In addition, no reason is apparent 

 why such an animal should breed as a yellow rather than as a tortoise- 

 shell or as a black. If such an animal was, immediately after fertilisation, 

 an XX (?) zygote, it is difficult to conceive how, even though its physio- 

 logical character and sex behaviour were altered to that of an XF (</) 

 individual, its chromosome content could likewise have been altered. 

 If its chromosome content was not altered, it remained an XX individual. 

 Since, however, it was physiologically male, it could of course, only be 

 mated with normal XX individuals ( $ ? ). A mating of XX with XX 

 should have given only XX {%) offspring. The fertile tortoise-shell 

 male, however, sired both male and female offspring, according to Don- 

 isaster's statement \ 1913, p. 19^ 



Before entering into a series of breeding experiments to determine 

 the existence of non-disjunction in cats, or attempting to collect material 

 for testing the hypothesis of hormone action, it should therefore be taken 

 into consideration that the following situation exists: The hypothesis 

 of non-disjunction, proposed by the writer, while admittedly more difficult 

 of experimental proof than that described by Doncaster, involves no 

 fundamental changes in the chromosome mechanism of sex determi- 

 nation. Its most visionary phase involves continued irregular somatic 

 behaviour of coat colours already shown to be peculiar in this respect in 

 the tortoise-shell female cat. • 



1 Journal of Genetics, Vol. iii. 



2 There is some question even in the case of the one surely fertile male reported, but 

 had his progeny all been of one sex, the fact could scarcely have escaped comment, since 

 he produced many offspring. 



