SHORTER ARTICLES AND DISCUSSIONS 



THE TORTOISESHELL CAT 



In The Journal of Genetics (June. 1913), Doncaster has sum- 

 marized genetic data dealing with the tortoiseshell cat. The 

 records are collected from fancy breeders and from the work of 

 Dr. C. C. Little. 



Aside from certain disputed points the inheritance is in ac- 

 cordance with simple sex-linkage and is analogous to the human 

 defects — color-blindness, night-blindness, ny>tagmus. and hemo- 

 philia, and to the thirty or more sex-linked factors of Dmstijihihi. 



If the factor for yellow be represented by Y and its allelo- 

 morph, the factor for black, by B, the lack of either by b, the 

 sex factor by X, and the allelomorph of X by x, the normal 

 zygotic possibilities are as follows: YX — bx = yellow male. 

 BX — bx = black male. YX — YX = yellow female. BX — 

 BX = black female. YX — BX = tortoiseshell female. 



It is obvious then that there can be but two classes of males, 

 while there are three classes of females. Difficulties arise when 

 it is attempted to explain the occurrence of black females pro- 

 duced either by the mating of a black female to a yellow male 

 which should give only tortoiseshell females and black males, 

 or by the mating of a tortoiseshell female to a yellow male, 

 which should give only tortoiseshell and yellow females and 

 black and yellow males. The occurrence of the rare tortoiseshell 

 male is also the cause of considerable difficulty. In one mating 

 out of seventeen of yellow females to yellow males there were 

 produced three tortoiseshell females. There are recorded in 

 addition from the seventeen matings forty yellow females and 

 forty-eight yellow males which arc in agreement with expectation. 



In order to explain these discrepancies it is suggested that 

 possibly the linkage of Y with X is not absolute. Yellow males 

 may then produce gametes bX and Yx in addition to the normal 

 or more frequent gametes YX and bx. (Jamete bX is female 



bearing. The latter gamete should produce a lorloisosh.-ll male 

 when it meets an egg BX. 



On this hypothesis we should expect the tortoiseshell males to 

 be as frequent as the anomalous black females from yellow 

 fathers. From the matings recorded there are eighteen anoma- 



