A CHANGE IN THE BAR GENE OF DROSOPHILA INVOLV- 

 ING FURTHER DECREASE IN FACET NUMBER 

 AND INCREASE IN DOMINANCE.* 



By CHARLES ZELENY. 



{From the Zoological Laboratory of the University of Illinois, Urbana.) 



(Received for publication, July 15, 1919.) 



As part of a study of the factors controlling eye facet number in 

 Drosophila melanogaster , selection has been carried on with a view 

 to the determination of the germinal changes appearing during the 

 course of selection. One of the most interesting of these changes 

 occurred during the second generation of downward selection in the 

 white bar stock. An exceptionally "low" male of this generation was 

 shown to possess a changed gene with a marked increase in domi- 

 nance. This individual appeared on November 20, 1917, and had 

 but 19 facets, while the mean of its 62 brothers was 82.6 facets with 

 a range of 41 to 134. With class sizes such that the range of a class 

 is 10 per cent of its mean this represents a departure of —16.80 10 

 per cent class units from the mean of the males of the unselected bar 

 stock, while the departure of the brothers of the mutant is only — 3.44 

 units. The new stock derived from the third hybrid generation of 

 a mating of the mutant with a sister possesses the characteristics of 

 the original male, and at the present writing (May 10, 1919) has 

 remained without change for nearly 18 months except for the ap- 

 pearance of a few additional mutants. 



The name ultra-bar has been given to the new character. Its 

 symbol, B^^ indicates that ultra-bar is a dominant allelomorph of 

 bar. Full-eyed (wild- type) females at 27°C. have an average facet 

 number of 810.6, bar females of the second low selected generation 

 have 61.8 facets, and ultra-bar females 22.0 facets. The correspond- 

 ing numbers for males are respectively 849.8, 75.6, and 23.0. 



*Contribution from the Zoological Laboratory of the University of Illinois, 

 No. 140. 



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