62 MENDELISM AND 



establishes the female condition. This is the same 

 difficulty which I pointed out above in connection 

 with the Mendelian theory that the female was 

 heterozygous and the male homozygous for sex. 

 Dr. Wilson points out that in the bee, where fertilised 

 eggs develop into females and unfertilised into 

 males, we should have to assume that the X chromo- 

 some in the female gamete is a female determiner 

 which meets a recessive male determiner in the 

 X chromosomes of the sperm. When reduction 

 occurs, the X 9 must be eliminated since the reduced 

 egg develops always into a male. But on fertilisa- 

 tion, since the fertilised egg develops into a female, 

 a dominant X 9 must come from the sperm, so that 

 our first assumption contradicts itself. 



Dr. Wilson, T. H. Morgan, and Richard Hartwig 

 have therefore suggested that the sex-difference 

 as regards gametes is not a qualitative but a 

 quantitative one. In certain cases there is no 

 evident quantitative difference of chromatin as a 

 whole, but there may in all cases be a difference 

 in the quantity of special sex-chromatin contained 

 in the X element. The theory put forward by 

 Wilson then is that a single X element means ijer se 

 the male condition, while the addition of a second 

 element of the same kind produces the female 

 condition. Such a theory might apply even to 

 cases where no sex-chromosomes can be distinguished 

 by tlie eye : the ova, in such cases (probably the 

 majority), might also have a double dose of sex- 

 chromatin, the males a single dose. This theory, 

 however, is still open to the objection that the 

 female gametes before fertihsation, and half the 

 male gametes, have the half quantity of sex- 



