GENETIC INTERSEXUALITY IN DROSOPHILA 43 



contained one full set of chromosomes and part or all of an 

 extra set. The diploid (2N) eggs fertilized by X-sperm gave 

 rise to 3N females; fertilized by Y-sperm they gave the 

 intersexes which were 2X:3A as contrasted with the 2X:2A 

 normal female (X=X chromosome; A=one haploid set of 

 autosomes). 



These observations made it clear that sex was determined 

 not, as had been thought, by the presence of one X or two, 

 but by the balance between the X and the autosome material, 

 by the genie balance. Dobzhansky and Bridges (1928) car- 

 ried this w^ork to its conclusion to find that X>A, i.e. that 

 the net male-determining tendency of a set of autosomes is 

 less than the next female-determining tendency of an X. 



iX:2A=a male 

 2X:2A=a female 



If the female-determining tendency of the sex-determin- 

 ing genes in an X-chromosome is represented by the figure 

 100, then the net male-determining tendency of the sex- 

 determining genes in a set of autosomes is of the order of 80. 



iX:2A 



100 160 



2X:2A 



200 160 



The following abnormal types could be expected and 

 were to be explained as under: 



