434 



Genetics of Sex Determination 



once tried to interpret the facts with autosomal determiners of both 

 sexes, but we have seen that the experimental data disprove such 

 ideas.) In female hetcrogamety in animals with large eggs, showing 

 considerable predetermination, the balance mechanism can use F 

 determiners located solely in the Y-chromosome. This is probably the 

 case in the silkworm also, though a final conclusion cannot be drawn in 

 the absence of intersexes. Tazimas' ( 1943-1944 ) results are based upon 

 the production of different polyploid and aneuploid conditions in the 

 silkworm egg. Table 4 contains the following important combinations 

 (as assembled by Kihara, 1953): A, autosomes; X(Z), Y(W), sex chromo- 

 somes; — L, — M, — R, deficiencies in the left, middle section, or right 

 arm; X(L) and X(R), only the left or right arm, respectively, present; 

 X(R)Y, the attachment of X(R) to Y. 



TABLE 4 

 (From H. Kihara, 1953) 



The table shows that the presence of a Y (= W) produces a fe- 

 male in whatever combination. This could mean that the Y contains a 

 very strong female determiner. But this could not act via cytoplasmic 

 predetermination: otherwise, all males should be intersexes (at least). 

 Another possibility is that the basic genetic mechanism is the converse 

 of that in Drosophila, F in the autosomes and M in the X, but with 

 the addition of a powerful female enhancer in the Y. We shall find 



