DECEEASE IN SEXUAL DIMORPHISM OF BAR- 

 EYE DROSOPHILA DURING THE COURSE 

 OF SELECTION FOR LOW AND HIGH 

 FACET NUMBER! 



PROFESSOR CHARLES ZELENY 

 University of Illinois 



In the bar-eye race of Drosophila the mean eye facet 

 number of the males is higher than that of the females, 

 though there is an overlapping in range as shown in 

 Table I. In the unselected white bar stock used as the 

 starting point of a series of selection experiments this 

 dit¥erence amounted to 6.12 factorial units, a factorial 

 unit being one that produces a ten per cent, change in 

 facet number. If this value were fairly constant it 

 would be possible in treating the selection data statis- 

 tically to reduce the facet values of the two sexes to a 

 common basis in much the same way that Galton obtained 

 a mid-parental value in his studies of the inheritance of 

 human stature. Such a procedure was followed by 

 Zeleny and Mattoon (1915)2 their paper on selection 

 in red bar-eye. In attempting to apply the same method 

 to the white bar series it was discovered that the differ- 

 ence between the two sexes is not constant but decreases 

 during the course of selection. It is therefore not prac- 

 ticable to apply a constant coefficient for the reduction of . 

 the value of one sex to that of the other. 



The selection experiment in question started with a 

 white bar stock which had been obtained by crossing 

 white full-eye to bar-eye. Single pair, brother and sister, 

 matings were adhered to with a few breaks due to steril- 

 ity. In the low line the lowest available virgin female 



-Zeleny, C, and Mattoon, E. W., 1915, "The EiYo^-t ef S.-leHiini upon 

 the 'Bar Eye' Mutant of Drosophila," J. Exp. Zool., 19: 51-3-529. 

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