254, THE THEORY OF THE GENE 



genes mutate why not sex-genes, if there are such specific 

 genes 1 



There is, in fact, one certain case of the occurrence of 

 an intersex that arose by a mutant change in the second 

 chromosome of Drosophila. Sturtevant (1920) studied 

 this case, and found it due to a change in genes in the 

 second chromosome. The female is turned into an inter- 

 sex. Unfortunately, tlie evidence does not show whether 

 or not a single gene only was affected. 



It is apparent, from what has been said, that while we 

 can interpret the sex-determining formulae in terms of 

 genes, we have no direct evidence, at present, that there 

 are any specific genes for maleness and femaleness. 

 There may be such genes, or it may be that sex is deter- 

 mined by a quantitative balance between all the genes. 

 But since we have much evidence that the genes differ 

 amongst themselves very greatly as to the kind of effects 

 that they produce, it seems probable, I think, that certain 

 genes may be more influential as sex differentials than 

 are other genes. 



Intersexes in the Gypsy Moth. 



Goldschmidt has carried out an extensive series of very 

 interesting and important experiments in the production 

 of intersexes in racial crosses of the gypsy moth. 



When the female of the common European gypsy moth 

 (Fig. 140a, b) is crossed to a Japanese male, equal num- 

 bers of male and female offspring are produced. When 

 the cross is made the other way the sons are normal, but 

 the daughters are intersexes or male-like females (Fig. 

 140c, d). 



Later Goldschmidt carried out an elaborate series of 

 crosses between the European species and several Japa- 

 nese species and also between different races of Japanese 

 varieties or species. The results may be arranged in two 



