132 



stitution of the other was tested. All 

 the experiments here described, on 

 "bar-infrabar" (figure 10), concern 

 this mutant gene. The stability of this 

 new type in the male has also been 



STURTEVANT 



tested. Matings of bar-infrabar males 

 to attached-X females (also differing 

 in at least one other sex-linked gene) 

 have produced 9042 non-disjunctional 

 sons,— all of them bar-infrabar. 



B' 



fBf,, 



Table 10 



9 XfBh$ 



The double-type male of table 11, cussed below under the name "infra- 

 which resembled those from table 9, bar-bar." 

 was tested. His descendants are dis- These new double types have made 



Table U 



iB^iu 



9 XfB^L $ 



it possible to devise crucial tests of the first test made was that of bar-infrabar 

 theory of unequal crossing over, over round. Tables 12 and 13 show 

 which may now be described. The the results obtained. In addition one 



Table 12 



fBB 



T 9 Xfh$ 



I u 



