18 Sex- Limited Inheritance in Cats 



birth, others that mistakes may be made. In some cases at least these 

 blues grew up and seem to have been undoubted blues, and I know of 

 no case of two blues mated together giving creams, as should happen if 

 an apparent blue may ever be heterozygous for cream. In any case, 

 the few black females from yellow sires, about which there appears to 

 be no doubt, seem to prove that the sex-limitation of the transmission 

 of yellow by the male is not absolute. 



Another point of considerable importance in connexion with the 

 comparison with the human cases is the ratio of the yellow to black 

 males in the offspring of tortoiseshell female x black male. As was said 

 above, in the offspring of transmitting females in the human cases, it is 

 generally believed that there is an excess of affected sons, but Lenz 

 regards this as due to the fact that a transmitting woman can only be 

 identified by having at least one affected son, and that this inevitably 

 raises the apparent ratio of affected to unaffected. When only large 

 families are considered, this excess disappears in the case of Colour- 

 blindness and Night-blindness, but remains in the Nystagmus and 

 Haemophilia totals, chiefly owing to the very great excess of affecteds 

 in certain pedigrees, but it seems doubtful whether even in these 

 affections it can be regarded as genuine. In the Cat, in which the 

 " transmitting female " (tortoiseshell) is visibly different from the " non- 

 transmitting " (black), a small excess of " affected " (yellow) over black 

 is found (35 yellow : 29 black), but as in the human cases there is also 

 an excess of " transmitting " (tortoiseshell) over " non-transmitting " 

 (black) daughters, (21 : 12). The numbers are small, and further data 

 are required before they can be regarded as significant, but they give 

 no support to the suggestion discussed above that the excess of affected 

 males is due to partial coupling of the factor for the affection with a 

 sex-factor in the gametes of the transmitting female. 



One of the most interesting questions connected with the inheritance 

 of these colours in the Cat is the nature and origin of the rare tortoise- 

 shell males. Three of these are included in my records, one (a blue- 

 cream) from the mating yellow ^ with black $ , one from tortoise- 

 shell female by black male, and one from tortoiseshell female by yellow 

 male. Two tortoiseshell males are also recorded from this last mating 

 in a note in Fur and Feather for May 10, 1912. I know of no other 

 case in which the male parent was known ; the few others that I have 

 met with have been produced by tortoiseshell females by unknown sires. 

 It has been shown above that there is reason for believing that the sex- 

 limitation of the transmission of yellow by the male Cat is not absolute, 



