NOTE ON THE INHERITANCE OF CHARACTERS 

 IN WHICH DOMINANCE APPEARS TO BE 

 INFLUENCED BY SEX. 



By L. DONG ASTER, M.A. 



Fellow of King's College, Cambridge. 



A NUMBER of cases have been described, in which it appears that a 

 character is dominant in one sex, recessive in the other. Such cases 

 fall into two categories, according to whether the character concerned 

 is inherited in the normal Mendelian manner, or is sex-limited in its 

 inheritance. Examples of the former type are the homed character in 

 sheep (horns dominant in the male^), and probably the white colour in 

 the butterfly Colias (white dominant in the female') ; of the sex-limited 

 type examples are colour-blindness, hereditary nystagmus and haemo- 

 philia in man, and probably the orange colour in cats'. In the latter 

 class it has frequently been stated that the character concerned is 

 dominant in the male, recessive in the female. Taking colour-blind- 

 ness as an example, we find the following facts. A colour-blind man 

 married to a normal woman has usually only normal offspring ; his sons 

 do not transmit the affection, but his daughters transmit it to some of 

 their male children, as in the following scheme: 



^ X 9 i colovu*-blind man 



(J 9 X (J (J normal man 



i 6 9 9 9 normal woman. 



A colour-blind man married to the normal daughter of a colour-blind 

 man may have colour-blind daughters as well as sons, thus : 



I 



I 1 



i 6 f 9 



* Wood, Journ. Agric. Science, in. 1909, p. 145. 



* Geroald, Amer. Naturalist, 45. 1911, p. 257. In this case there is the complication 

 that homozygous white females have not been observed. 



3 Doncaster, Proc, Camb. Phil. Soc. xni. 1905, p. 35. Since the pablication of that 

 paper I have obtained evidence, not yet conclusive, that the inheritance of the orange 

 colour is sex-limited. Experiments to test this more fully are being made. 



