130 



STURTEVANT 



Table 5 



+ 



fBBf^ ? Xffu$ 



female gives 100 percent non-disjunc- 

 tion. This race, and others separate in 

 origin but having the same peculiarity 

 of attached X's, have been used to test 

 the mutability of bar in the male. If a 

 round-eyed female with attached X's 

 is crossed to a bar male, all the sons 

 get their X chromosomes from the bar 

 father and accordingly furnish a direct 



test of the mutability of bar in males. ^ 

 A total of 10,079 bar males has been 

 observed from such matings, with no 

 rounds or double-bars. There was, 

 however, one other male that had an 

 eye intermediate between bar and 

 round. This new type, called infrabar 

 (figures 7, 8, 9) has been shown to 

 represent a new allelomorph of bar. Its 



Table 6 



+ 

 fBfu 



9 XfUS 



somatic appearance will be described 

 in more detail later in this paper. 



Tests soon showed that infrabar be- 

 haved as a single unit in inheritance. 

 Bar can not be recovered from it, and 

 it shows the same linkage relations as 

 bar. The convincing proof that it 

 represents a modification of the bar 

 gene will appear below. 



Homozygous infrabar behaves like 

 bar in that it reverts to normal, and 

 also produces a new and more extreme 

 type, double-infrabar (figure 10), 

 analogous to double-bar. As shown in 



table 8, both these events are again 

 associated with forked-fused crossing 

 over. 



Of the three double-infrabar in- 

 dividuals, one was sterile, and one was 

 accidentally lost, but the constitution 

 of the other was established by breed- 



5 Occasionally the attached X's separate, 

 and a regular son carrying a maternal X is 

 produced. In the present series of experi- 

 ments this source of error was eliminated 

 by having the two maternal X's differ from 

 the paternal one in at least one other mutant 

 gene besides bar. 



