Mr Doncaster, On the Inheritance of Colours in Gats. 35 



On the Inheritance of Tortoiseshell and Related Colours in 

 Cats. By L. Doncaster, M.A., King's College. 



[Read 28 November 1904.] 



It is well known that Tortoiseshell cats are almost always 

 females, and it is commonly said that the corresponding colour in 

 males is orange (otherwise described as red or yellow). In the 

 hope of throwing light on certain other cases of varieties confined 

 to one sex I was led to inquire into the matter more fully, and 

 with that object wrote to a number of owners of pedigree cats 

 asking for further information. I received a considerable number 

 of replies, which are so closely in agreement that there can be 

 little doubt about the accuracy of the statements, and it is wholly 

 upon the evidence so obtained that this note is based. 



Tortoiseshell kittens may be obtained from the following kinds 

 of matings : 



(a) Tortoiseshell ? x Tortoiseshell J 1 . 



(b) „ x black or blue £ . 



(c) „ x orange <£. 



(d) Orange $ x orange </. 



(e) „ x black or blue </. 



(f) Black or blue $ x orange <£ . 



In all of these matings in addition to Tortoiseshells, kittens of 

 other colours may appear, viz. : 



(a) Tortoiseshell $ x Tortoiseshell £ gives Tort., orange, 



black. 



(b) Tortoiseshell $ x black or blue £ gives Tort. $ , orange 



J, black J,%. 



(c) Tortoiseshell % x orange <f gives Tort., orange, black. 



(d) Orange % x orange </ gives either Tort., orange (and in 



one case blue, see below) ; or, only orange. 



(e) Orange $ x black J 1 gives Tort. $ , orange £. 



(/) Black % x orange £ gives Tort., black (and probably 

 orange). 



(g) Black $ x black £ gives only black (or blue). 



From these facts it is clear that tortoiseshell is a heterozygous 

 form ; it is produced by mating orange with black, both of which 

 can be bred true, but in the rare cases when a tortoiseshell % has 



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