ON SEX-LIMITED INHERITANCE IN CATS, AND ITS 

 BEARING ON THE SEX-LIMITED TRANSMIS- 

 SION OF CERTAIN HUMAN ABNORMALITIES. 



By L. DONCASTER, M.A., 



Fellow of Kinff's College, Cambridfje. 



Sex-limited inheritance is now kno\\Ti to be a widespread pheno- 

 menon, but several problems of importance in connexion with it still 

 remain obscure. It has been shown to exist in Lepidoptera and Diptera, 

 in Birds and Mammals, and falls into two classes, according to whether 

 the sex-limited transmission is by the male or the female. In Abraxas 

 (Lepidoptera) and in the Fowl, Canary and Pigeon the female is found 

 to be normally heterozygous for certain characters, and with rare 

 exceptions transmits them to her male offspring only ; in Drosophila 

 (Diptera) and in Man and the Cat the male is similarly heterozygous 

 and transmits certain characters chiefly or only to his daughters. The 

 simple conclusion from these facts would be that in Lepidoptera and 

 Birds the sex of the offspring is determined by the egg, and in Diptera 

 and Mammals bj' the .spermatozoon. There is evidence, however, that 

 the sex-ratio in Drosophila is partly at least dependent on the female 

 parent^ and evidence pointing in the same direction has been brought 

 forward in the case of Man. It is plain therefore that a full knowledge of 

 sex-limited inheritance is of fundamental importance for the solution of 

 the problem of the determination of sex. It is also of great importance 

 from a somewhat different point of view. The hypothesis has been 

 widely accejDted that not only is sex determined by the so-called sex- 

 chromosomes, which have been chiefly studied in Insects, and are known 

 to exist in many other groups of animals, but also that the factors for 

 sex-limited characters are also borne by these .sex-chromosomes. Simple 



' Moenkhaus, W. J., .Tourn. Morphol. Vol. xxii. 1911, p. 23; Eawls, Biol. Bulletin, 

 XXIV. 1913, p. 11.5. [Morgan, Science, Vol. xxxvi. p. 718, Nov. 22, 1912, has given an 

 explanation of Miss Rawls's results which is not inconsistent with sex determination by 

 the spermatozoon in Drosophila. Note added March 5, 1913.] 



