282 Action of the Genetic Material 



as well as of production of specific intracellular and extracellular 

 products are based upon the stepwise syntheses to which the theory 

 refers. 



Even at this end, difficulties arise when we come to such active 

 substances as enzymes and hormones in the wider sense discussed 

 above. Are they also synthesized step by step, each step being in some 

 way controlled by one gene? Here again we meet the danger of 

 loose terminology, already discussed in detail (III 1). It is very 

 unfortunate that the Kiihn school, upon their discovery of the gene- 

 controlled synthesis of such pigment precursors as kynurenine, called 

 these precursors Genwirkstoffe, while they are only steps in the 

 synthesis of a completely inactive product to be deposited. Butenandt, 

 the great chemist who did the chemical work, still uses this term ( 1952, 

 1953), thus deceiving himself (and his non-geneticist readers) into 

 the belief that the pigment precursors are the active substances which 

 are the organs by which the genes control hereditary traits. Simul- 

 taneously, Ephrussi and Beadle used (and sometimes still use) the 

 term "hormones" for the same substances. Though I do not doubt 

 that they realize the danger of such terminology, I am afraid that 

 many biochemists and others not suflBciently trained in biology take 

 the term at its face value and assume that the secret of Genwirksto^e 

 has been exposed and that here my old theory (1920a) that genes 

 act by producing the hormones of differentiation has been demon- 

 strated. 



b. Relation to other ideas 



Let us return to the generalization. Pigments and plant colors 

 are good materials for Mendelian studies because they are easily 

 classified. In molds and bacteria the production of metabolites may be 

 grouped in the same category, thanks to the creation of ingenious 

 techniques by Beadle and Tatum (1941). But the hereditary control 

 of development in all its phases must entail much more complicated 

 processes. Though it is understood that in the end they will go back 

 somehow to a biochemical basis, it is diflBcult to believe that all genie 

 action begins and ends with one step in a biosynthesis and that 

 therefore all heredity can be compounded from such individual steps. 

 Although I realize that it is difficult to define exactly what more is 

 needed to understand genie action, still I am convinced that the one 

 gene — one function idea ( apart from the criticism of the gene theory ) 

 applies only to metabolites and their like (from the study of which 

 Beadle and his precursors, like Garrod, Onslow, Scott-Moncrieff, and 



