Different Genetic Possibilities within the Balance Theory 433 



cases only a single F or M locus exists, or a block of completely 

 linked loci or a more or less large set of individual loci (locus being 

 meant either in the classical sense or in the sense of heterochromatic 

 sections, if our interpretation turns out to be true). Thus the question 

 of one sex determiner versus many sex determiners, which once 

 seemed very important, is no longer of theoretical importance so far as 

 sex determination alone is concerned. We have already discussed an 

 example of assumed single sex determiners ( III 5 A b; Moewus' work ) , 

 to which we shall return. 



These remarks apply to sex determiners in the X-chromosome; 

 they may apply to the Y-chromosome also, as we shall see. (Tazima, 

 1943, found that in Bombyx only a small section of the Y was female- 

 determining. ) These remarks should apply also to autosomal sex 

 determiners. A good example is Drosophila, in which Bridges (1922) 

 first assumed that M determiners were distributed over all autosomes. 

 Later he found that haplo-, diplo-, triplo-IV did not affect sex or grade 

 of intersexuality, so that the fourth chromosome fell out. Then S. Bedi- 

 chek Pipkin showed, with the same method used by Dobzhansky and 

 Schultz (1934), that none of these are present in the second chromo- 

 some, as far as the experiments go. Thus only the third chromosome is 

 left, and nobody has thus far located the M factor or factors there. In 

 spite of these clear-cut facts, the multiple sex factors over all the 

 autosomes of Drosophila continue to be presented as a fact in general 

 discussions and in textbooks; even the presence of both F and M 

 factors in the autosomes are claimed without any factual basis. 



B. VARIANTS WITHIN THE BALANCE SYSTEM 



Much more important are the variants in regard to the chromo- 

 somal setup of the balance system. Basic differences are expected here 

 between forms with female and those with male heterogamety. 



a. Female heterogamety 



In female heterogamety, each egg before maturation contains a 

 Y-chromosome. Genetic properties of the Y can act in the growing 

 egg via predetermination through the cytoplasm. Thus an egg that 

 later will develop into a male was exposed to Y action during the 

 period of predetermination. Therefore, it is possible that the Y con- 

 tains female determiners which in the male without a Y take part in 

 the balance system because of their action before fertilization. We have 

 seen that this is so in Lymantria, where autosomal sex determiners 

 (but not modifiers!) have been completely excluded. (Winge, 1937, 



