THE MUTATED GENE 111 



We may interpret them by means of a simple diagram (Fig. 24), 

 based upon the following considerations. Different genie 

 combinations produce different percentages of scalloped and 

 normal, in orderly progression. As was pointed out before 

 (page 67), this must mean that there is a threshold beyond 

 which individuals are normal and a fluctuation that shifts part 

 of the population across this threshold. This threshold line 

 is found in the diagram as a definite time in development, beyond 

 which the wing remains normal, and the fluctuation of each 

 population is represented by the base line of the statistical curve 

 of variability. To the left of the threshold follow the different 

 degrees of scalloping from I = nicked to XI = no wing. The 

 unbroken lines represent the range of fluctuation for populations 

 of the different alleles and compounds (cf. Fig. 20, page 59). 

 In the experiments to be reported, the dominigenes were added 

 to all these genie combinations, and the broken lines represent 

 these combinations. We see here that the phenotype of all 

 the heterozygotes, homozygotes, and compounds up to homo- 

 zygous notched are shifted in a perfectly parallel way toward less 

 dominance of ± normal, i.e., to the left side of the diagram. This 

 regular behavior in the action of the dominigenes is found up to 

 class VI of scalloping but not beyond. Class VI is the maximum 

 scalloping possible if degeneration sets in after pupation, and 

 therefore the dominigenes in this case act only upon processes 

 after pupation, i.e., after evagination of the imaginal disks. The 

 important point is now that the dominance-shifting action 

 of the dominigenes works in a consistent quantitative way upon 

 different heterozygotes as w r ell as homozygotes of lower alleles: 

 the shift is then not a shift of dominance but a shift in a process 

 that is responsible for dominance as well as for the phenotype 

 of the allelic series and their compounds (also for the phenocopic 

 effect). Since it was stated earlier that these phenotypes are. the 

 product of different rates of one and the same reaction (viz., 

 the production of growth substances, or of lytic substances. 

 see page 59), it follows that dominance also is a subphenomenon 

 of the same system of reactions of different speed: dominigenes 

 change this speed or one of the concomitant processes controlling 

 threshold, etc. (see model Fig. 23). with the same quantitative 

 effect upon the result as different alleles or temperature shocks 

 produce. Only a system of the type of our modc^l (Fig. 23) will 



