14 Sex- Limited Inheritance in Cats 



also disappears in the case of Colour-blindness and Night-blindness, but 

 remains almost unaltered in the Nystagmus totals. In the case of 

 Haemophilia it varies greatly; in some families there is in each 

 fraternity a great excess of affecteds, in others equality or deficiency ; 

 the totals when only large fraternities are included show a smaller 

 excess than when all fraternities of every size are added together. It 

 is the possible existence of this excess of affected individuals in the 

 offspring of transmitting females which is chiefly of importance for the 

 purpose for which the enquiry was undertaken. For it has been pointed 

 out above that in some cases at least sex-limitation is not absolute, but 

 is partial like gametic coupling of other characters, and it seems at 

 least possible that the excess of affected over normal males among the 

 sons of transmitting females might be due to partial coupling of the 

 factor for the disease with a sex-factor, among the gametes of the female 

 parent. We know that the factor for the affection is absolutely or 

 almost absolutely coupled with a sex-factor in the gametes of the 

 affected male, for he transmits the factor only, or almost entirely, to his 

 daughters, his sons being very rarely if ever affected. If then we also 

 found that a woman bearing this factor transmitted it chiefly to her 

 sons, we should have absolute sex-limited transmission by one sex, 

 and partial sex-limited transmission by the other sex, in the same 

 species. A basis would thus be provided for a reconciliation of the two 

 types of sex-limited inheritance, exemplified respectively by Abraxas 

 and Birds on the one hand, and by Drosophila and Mammals on the 

 other. 



If this were the case, the high ratio of affected sons of a trans- 

 mitting woman should be associated with a low ratio of transmitting 

 to non- transmitting daughters. My material gives no evidence that 

 this is the case ; although the data for determining whether the 

 daughters of a transmitting woman do or do not transmit are very 

 inadequate, they suggest that the transmitting daughters are more 

 numerous than they should be if the excess of affected over normal sons 

 were due to gametic coupling of the factor for the disease with a sex- 

 factor, in the gametes of the transmitting mother. The families which 

 have an exceptionally high ratio of affected males also have a high ratio 

 of transmitting daughters, instead of a lower ratio as would be expected 

 on the gametic coupling hypothesis. It is hardly possible, therefore, 

 with the data at present available, to come to any definite conclusion 

 about the nature of the transmission of these human abnormalities. It 

 can only be said that there is in some pedigrees an excess of affected 



