374 Action of the Genetic Material 



same time. The different mean wing sizes are roughly estimated (e.g., 

 No wing being one-eleventh of the normal size). These values are 

 found at the right ordinate together with the names of the alleles and 

 a classification of the scalloping effect: I is just a small nick; XI, the 

 No-wing type. To the right of this the range of variation for all effects 

 is indicated, as found in experiments at 25° C. I do not maintain that 

 this diagram represents what actually happens; the real causative 

 agent may be something very different from a growth substance. I do 

 claim, however, that it is a model for the type of what must be hap- 

 pening in cases of the kind studied, namely, a regular series of genie 

 potencies leading to a just as regular series of phenotypes. It seems 

 hardly possible that the facts can be explained simply by any theory 

 that does not entail seriated and graduated effects upon the kinetics of 

 genically controlled processes. Thus, this diagram becomes a rather 

 universal model of genie actions that are not of an all-or-none type 

 (see III 4 C), that is, simply biochemical. 



Practically all degrees of scalloping from vg to + can be obtained 

 if vg/vg is bred in high temperatures near the temperature shock 

 zone; this fact was known in the early days and has been much 

 studied by Harnly (see 1942). This proves, of course, that the anlage 

 of the vg wing still has all developmental potencies including the 

 complete pattern of venation. Further, speeding up of some reaction 

 by temperature treatment more or less prevents the vg reactions 

 covered in our diagram from taking place, or prevents them from 

 reaching the threshold levels, or interferes in some way with normal 

 growth. It is obvious that the facts fit very well into such a scheme 

 of genie action as that of figure 19, and are very difficult to explain 

 otherwise. Actually this is the same situation as for the temperature- 

 dependent mutants of Neurospora (see III 4 C a), except that here the 

 parallelism to the allelic series makes it almost certain that the ex- 

 planation involves the kinetics of a process. As I mentioned before, it 

 was just these temperature-dependent mutants of Neurospora that 

 led to skepticism toward the one gene — one synthetic step concept in 

 favor of some action upon the kinetics of chains of reaction. 



Only now we come to our experiments, which bear out the cor- 

 rectness of the entire trend of discussion in the present chapter. It is 

 a quantitative study of the vg series in the presence of dominance 

 modifiers. Normal wings are completely dominant over vestigial under 

 standard conditions (25° C). Three dominance modifiers were isolated, 

 located in the first, second, and third chromosomes, respectively, in 

 the presence of which dominance is shifted toward vestigial. If two 



