Genie Control of Development 377 



Group III contains the compounds of vg and vg^'* with the low allele 

 vg"' with and without dominance modifiers. Here the same shift is 

 found, but it is very small. The last group, IV, contains the compounds 

 of vg and vg^" with vg"°, all of which show the wing reduction taking 

 place visibly before pupation. Here the effect is no longer clear. 



Thus we see that the dominance-shifting action of the modifiers 

 works in a consistent, parallel, quantitative way upon homozygotes, 

 heterozygotes, and compounds of the lower alleles. Therefore, the 

 shift must be based in all cases upon a simple and in its nature identi- 

 cal, quantitative effect upon the processes or reactions controlled by 

 the homozygotes, heterozygotes, and compounds of vg and its alleles. 

 If we turn again to the representation of the vestigial action in terms 

 of speed of reactions and quantities of end products, as represented 

 in figure 19, we realize that dominance is a potency effect, ceteris pari- 

 bus, like multiple allelic effects and dosage effects. I think that so 

 consistent a group of facts requires an explanation in terms of genie 

 action controlling in a quantitative way some phase of the kinetics of 

 production of active end products, whatever their nature. 



One additional point should be mentioned. Blanc has demon- 

 strated that two of the dominance modifiers are identical with the 

 mutants purple ( darker eye color ) and facet ( rough eyes ) ; this makes 

 these modifiers loci with pleiotropic action upon completely different 

 characters. (Also in rodents, certain pigment mutants affect mor- 

 phological traits; see Griineberg's book. ) This again raises the question 

 of qualitative versus quantitative action. The eye color purple is 

 probably a quantitative deviation of pigment formation. The rough 

 eyes of facet do not suggest a qualitative basis, though Hinton and 

 Ellis (1950) could produce the character reversibly by a nutritional 

 deficiency. But practically all phenocopy experiments, with whatever 

 agent, produce rough eyes most easily. Thus the facts mentioned can 

 hardly be cited in favor of qualitative action of alleles. 



We are analyzing here the theory of genie action, and therefore 

 the much discussed problem of the origin of dominance enters our 

 deliberations only so far as it has to do with the theory of genie action. 

 Actually, any theory of the origin of dominance can be no more than 

 purely formalistic if a physiological system of genie action controlling 

 dominance is not made the basis of discussion. It is well known that 

 Fisher ( 1928-1932; see 1935 ) developed a phylogenetic and statistical 

 theory of dominance of wild type over mutations, involving a selec- 

 tion of modifiers that shift the phenotype of the heterozygote toward 

 wild type, because the wild type has the selective advantage which 



