L. DONCASTBR 19 



since a small proportion of black females are produced from yellow sires, 

 and if this is so, there should theoretically be as many cases in which a 

 yellow male transmits yellow to his sons, as there are of his failing to 

 transmit it to his daughters. I know of no satisfactory record of a 

 yellow male mated to a black female having yellow sons, but suggest 

 that the tortoiseshell male is produced when, exceptionally, yellow is 

 transmitted by a yellow male to a son'. 



Very little is known of how a tortoiseshell male transmits cplour- 

 factors to his offspring. The few breeders who possess them commonly 

 mate them to tortoiseshell females, in the belief that this is the most 

 likely mating by which to produce tortoiseshell male offspring, and I 

 know of only one mating with a black female, which is the one required 

 to test the matter thoroughly. In this one case the female was not 

 kept in confinement, so that although the pairing was seen, the 

 parentage of the kittens cannot be regarded as certain ; the only 

 recorded kittens were a black male and a tortoiseshell female. When 

 mated with tortoiseshell females, tortoiseshell males appear to behave 

 like yellows, giving yellow and black male, tortoiseshell and yellow 

 female offspring. Sir Claude Alexander, who has made many such 

 matings with one of his well-known specimens, writes of this tortoise- 

 shell male that with unrelated tortoiseshell females he " sires tortoise- 

 shells freely," but that with his own tortoiseshell daughters he gives 

 chiefly yellows, with only an occasional tortoiseshell female or a black. 

 Unfortunately, no record of the sex of these kittens appears to have 

 been kept ; no tortoiseshell males were produced. 



The facts, then, as far as they are known, of the transmission of the 

 yellow colour in the Cat, may be summarised thus. In the female the 

 factor for yellow when homozygous produces orange (or cream when 

 dilute); when heterozygous produces tortoiseshell. In the male the 

 presence of the yellow factor normally produces orange (or cream), but 

 such males are not homozygous, for in general they transmit the yellow 

 factor to their daughters only. Exceptions to this rule, however, occur, 

 not apparently very rarely, for black females from yellow sires are 

 frequently recorded. Less common are tortoiseshell males, about which 

 little is known, except that they may apparently derive the yellow 

 factor from either parent, and that there is no recorded case of their 

 having tortoiseshell male offspring. 



Until more data are collected, it seems of little value to attempt t<j 

 express these facts in a factorial scheme, for no means of testing such 



' See also p, 21 below. 



2—2 



