16 Sex-Limited Tnheritance in Cats 



females, showing that a female heterozygous for orange transmits the 

 orange factor to some kittens of both sexes. The colours cream and 

 blue appear to be dilute forms of orange and black, and to be inherited 

 similarly. In what follows I shall use the term " yellow " to include 

 orange and cream, " black " to include black and blue, tortoiseshell to 

 mean a mixture of yellow and black, and, when necessary, "blue-cream" 

 to describe the dilute tortoiseshell. The data given are derived almost 

 entirely from correspondence with numerous breeders, but include the 

 litters given by Little in the article in Science referred to. In the 

 information obtained from breeders I have made every effort to insure 

 that all inaccuracies are eliminated, but it is possible that a few 

 mistakes may have been included. Where I have good cause for 

 doubting the accuracy of a record, it has been omitted from the 

 tables. 



A summary of the data collected with regard to the inheritance of 

 the yellow and black colours in Cats is given in the accompanying 

 table. It is noticeable that the divergences from equality of the two 

 sexes are similar in kind to those observed in the case of human sex- 

 limited diseases, where, however, as has been seen, it is doubtful 

 whether they are significant. In the offspring of yellow male mated to 

 black female there is some excess of females (61 $ : SOt/*), as is also the 

 case among the offspring of men affected with one of the four diseases 

 mentioned previously ; among the offspring of tortoiseshell females by 

 black males there is a considerable excess of males (67 (/* : 35 J ), as has 

 generally been found to be the case among the children of women who 

 transmit the diseases. 



Another point of great importance is that there is evidence that 

 the sex-limitation of the transmission of the yellow factor by the male 

 is not absolute, for thirteen black or blue females are recorded from the 

 cross yellow male mated to black or blue female, five from yellow male 

 by tortoiseshell female, and three tortoiseshell females from one mating 

 of yellow male by yellow female. It should be mentioned that the 

 majority of the eighteen black or blue females from yellow sires were 

 blues, and it is possible that the simple explanation that sex-limitation 

 is not absolute, is not the true one in every case. Apart from the 

 possibility that the sex may have been wrongly recorded in some 

 instances, it is not completely certain that a young kitten may not 

 sometimes be recorded as a blue when it is in reality a blue-cream. 

 The breeders of whom I have enquired on this point are not agreed ; 

 some say that blue-creams are always easily distinguished from blues at 



