376 Action of the Genetic Material 



scalloping I-XI and wild type beyond I. Since there can be a fluctua- 

 tion into wild type and, in addition, different (genetic) grades of wild 

 type, the abscissa simultaneously indicates development proceeding 

 from left to right, with the decisive time of pupation ( decisive, because 

 we tested the morphology of the anlage at this time) indicated by a 

 broken ordinate. Between scalloping grade I and wild type lies the 

 threshold for complete dominance shown by wild type, indicated by 

 an ordinate. This means, for example, that 100 per cent dominance is 

 located to the right of this line, but if 1 per cent of the heterozygotes 

 show scalloping in the presence of modifiers, 1 per cent of the curve of 

 variation of all individuals of this composition will be found left of 

 the threshold line. We represent now the range of variation of all 

 combinations as a horizontal line; full lines indicate ordinary com- 

 pounds; broken lines, the same plus dominance modifiers. Thus we 

 chart not only dominance modification in vg/+ or the compound 

 vg/vg"', and so on, but also eventual shift of phenotype of the homo- 

 zygotes in the presence of the dominance modifiers. If such a shift 

 were found, it would be a decisive result, because it weuld show 

 that both dominance and multiple allelism are based here upon the 

 same processes of potency of action. 



When the lines in the diagram representing the base line of a 

 curve of variation are located to the right of the theshold, that is, 

 within normality, the range of fluctuation is, of course, only extrapolated. 

 The same is true when part of the individuals are scalloped, left of the 

 threshold line, and part are normal; in this case what is left of the 

 threshold line is actually observed; but right of the threshold, extra- 

 polated. It is now known that the scalloping classes I-V can be pro- 

 duced though the wing is still normal at the time of pupation; while 

 classes VI-X already show increasingly reduced wings at pupation 

 time. This is the reason for putting into the diagram the pupation time, 

 which is our mark of the time of action of different combinations. 

 The base lines for the range of fluctuation of the resulting phenotypes 

 show that for all scalloping classes up to class VI, the dominance 

 modifiers shift all homozygotes, heterozygotes, and compounds in the 

 same way toward the left, that is, toward dominance of vestigial, and 

 so on, as the comparison of the full and broken lines for each type 

 shows, with an ascending order from the lowest, the vg"'/-H hetero- 

 zygote, shifted just beyond the threshold of normality, to the highest 

 combination vg°Vvg"", shifted about two classes. In group II, only the 

 shifting of dominance for the vg and vg^"' heterozygote is represented, 

 which shows a still more extreme shift in the presence of the modifiers, 



