36 SEX-DETERMINATION 



female intersexuality is transmitted in the X-chromosomes, 

 and the resuhs are exactly what would be expected if this 

 intersexuality-producing 'strength' is a property of the 

 X-chromosome of the 'strong' race. They show, further, 

 that the X-chromosome of the 'weak' race carries the 

 determiner of this property 'weakness', and, finally, they 

 show that the F. i females behave like pure 'weak' females. 



B. F.I strong $ x weak cJ gave $$ all normal; ^(^ all normal 



F.2 strong $ x weak (^ gave $$ all normal; (^<^ half normal, 



half intersexual 

 Backcross. Strong $ x F.i (strong $ x weak cJ) (^ gave ?? all 



normal; ^<^ all normal 

 Backcross. Strong $ x F.i (weak ? x strong o) o gave 2$ all 



normal; SS all normal 

 Backcross. F.i (strong $ x weak (J) $ x strong (J gave $$ all 



normal; c^cJ all normal 

 Backcross. F.i (strong $ x weak cj") $ x weak (^ gave ?? all 

 normal; dl*c? all intersexual 



These results show that the property 'weakness' (weak 

 males) is transmitted in their X-chromosomes, that in these 

 combinations two 'strong' X-chromosomes or one 'strong' 

 and one 'weak' produce normal males, two 'weak' X-chromo- 

 somes produce intersexual males, and that all the mothers 

 in this series behave as 'strong' females whether they belong 

 to a pure strong race or whether they be hybrids out of a 

 'strong' mother and a 'weak' father. 



If the two lots of results are considered together it is seen 

 that 'strength' and 'weakness' are, firstly, characters, the 

 determiners of which are carried in the X-chromosomes of 

 the respective races, and, secondly, that 'strength' and 

 'weakness' are properties which are inherited only in the 

 female line. Sex is determined by a definite relation or 

 balance between the respective 'strength' or 'weakness' of 

 one type of sex-determining factors inherited maternally 

 and the other type which are transmitted within the 

 X-chromosomes. It is seen, further, that the combination 

 of the 'weak' maternally inherited determiner with a 

 'strong' X-borne determiner shifts the female (XY) toward 

 maleness, whereas the combination of a 'strong' maternally 



