Different Genetic Possibilities within the Balance Theory 447 



Lymantria, but they are so strong that any egg with a Y will be 

 female, whatever the number of X, which contain the male deter- 

 miners. As XX individuals are males, the strong Y which is present in 

 all eggs before fertilization cannot have a predeterminative influence, 

 for otherwise all males would be intersexual. Thus the old Correns 

 formula (changed for female heterogamety), MM = $, MF = 9, 

 F > M, could be employed here so long as no male intersexuahty is 

 known. This problem awaits further clarification. 



We might attempt to explain both the Lymantria and the Bombyx 

 situation in the same way we tried to understand that of Melandrium, 

 forgetting for the moment the potential monoecism of this plant. This 

 means the assumption that F is an autosomal property; M is located 

 in the X-chromosomes; and a strong enhancer for femaleness, in the 

 Y-chromosome. In favor of such an assumption could be cited the fact 

 that triploid intersexuahty in moths possibly follows the Drosophila. 

 scheme (of course, with the changes due to female heterogamety). 

 I said "possibly" because we do not know much about the Y-chromo- 

 some in most cases. But where no Y is present (the XO type in 

 Solenobia) , the Drosophila type must obtain. The facts regarding the 

 silkworm may be expressed in the same terms as in Melandrium, that 

 is, with a strong Y-chromosomal enhancer. In this case, the assumption 

 of a predetermining action of the Y in the eggs destined to become 

 males is superfluous, because autosomal F (female determiners) are 

 present, though they have not yet been demonstrated. However, in 

 Lymantria such a theory would be very difficult. In order to explain 

 the experiments on the production of male and female intersexuahty, 

 we need both male and female determiners of different valency. If F 

 were located in the autosomes, and the Y carried an enhancer for 

 femaleness, the autosomes would have to carry F's of different potency 

 in order to explain male intersexuahty in the absence of a Y. But the 

 facts of female intersexuahty require different potencies of the female 

 "enhancers" in the Y. Finally, the facts of the complex crosses and the 

 Hokkaido replacement experiments (discussed in IV 2) exclude a 

 participation of autosomal female determiners (although autosomal 

 modifiers have been demonstrated). Thus the genetics of sex deter- 

 mination is probably of the Lymantria type, as described, wherever 

 female heterogamety exists with the presence of a Y-chromosome; of 

 the Drosophila type, in male heterogamety and in female XO hetero- 

 gamety; and of the Drosophila type plus Y-chromosome enhancers, in 

 special cases like Melandrium. There is, of course, no reason to expect 

 that the details are the same in all organisms, in view of the fact that 



