02 PHYSIOLOGICAL GENETICS 



Upper parallel indicates the lytic threshold in the presence of Mn. 

 A parallel to this would be the action of the dominigenes (or 

 temperatures) upon the up-curves. 



It is clear that we could use the graph for the phage also to 

 describe the vestigial case, viz., under the former assumption that 

 the genes produce here a lytic substance which acts upon the wing 

 as soon as a threshold value is reached. The main curve of 

 Krueger's graph would then represent the grow r th and subsequent 

 lysis of the wing; his curves for phage production w r ould be the 

 curves for production of the lytic substance; the initial concen- 

 tration of phage would be the different alleles of vg, and the 

 manganese curves would represent the action of modifiers which 

 will be studied later. The phage model then contains exactly 

 the system that we postulated for gene action and especially the 

 vestigial case: a growth curve; an onset of destruction at definite 

 times ; a proportion between this time and the basic concentration 

 (see later the theory of multiple alleles); and threshold values, 

 which might be modified by other substances produced by modi- 

 fying genes. The parallelism, if not more significant, shows at 

 least one thing: The type of genie actions as derived from the 

 author's work is actually found in comparable processes in nature. 



It ought to be added that Mohr in his study of this allelo- 

 morphic series drew some similar conclusions, in so far as it was 

 possible without knowledge of the development. He speaks 

 of the different potencies of the alleles in producing the respective 

 amounts of scalloping and assigns definite numerical values to 

 these potencies, a method of description that was introduced by 

 Goldschmidt (1912) in his work on the potencies of sex genes. 

 He gives the highest value to the potency for production of the 

 Normal wing (30 for one gene) and the lowest (0 to one No-w r ing 

 gene) as estimated, of course, from the phenotypical result. 

 These values are found at the base of Fig. 19. The threshold 

 for the first indication of a Nick, then, is found at potency 37. 

 He discusses further the probability that these potencies act by 

 controlling reaction velocities. 



It is probable that similar cases may be found in plants, as 

 might be inferred from Van Overbeek's (1935) work. He 

 studied the recessive character nana in corn which causes an 

 inhibition of growth of the mesocotyl. He studied the behavior 

 of the growth hormone (auxin) in this mutation and found that 



