Primary Actions 283 



Haldane, derived the idea). To this should be added such genically 

 controlled specific substances, not of the metabolite type, which are 

 found within the organism, for example, the specific antigens and 

 hemoglobin. Both of these are gene-controlled, or, in more cautious 

 language, are not produced or are produced with a wrong constitution 

 (hemoglobin after Pauling et al., since 1949) if a mutant locus is 

 present. 



Before mentioning other possibilities, it is fair to state that the 

 one gene — one enzyme or one gene — one function hypothesis has been 

 defined in a somewhat broader sense by Horowitz ( see 1951 ) . He argues 

 thus: the concept is that of a gene whose sole activity (in addition to 

 self-duphcation ) is that of functioning in the synthesis of a particular 

 enzyme or enzyme precursor. Other loci may, however, also be con- 

 cerned directly with the formation of the enzyme. The hypothesis does 

 not imply that the final phenotypic expression of a mutation is neces- 

 sarily restricted to a particular structure or function of the organism. 

 The ultimate effect of a mutation is the result of an enormous magni- 

 fication of the initial gene change, brought about through a system of 

 reactions which, originating at the gene, rapidly branches out in vari- 

 ous directions and coalesces with similar networks derived from other 

 loci, to form a reticulum of as yet indeterminate extent and complexity. 

 It is impossible to decide from the end effects alone whether the gene 

 has one or many primary functions, since, on either assumption, a 

 complex pattern of effects is expected in most cases. A mutation which 

 induces a deficiency of an amino acid must secondarily affect the 

 synthesis of virtually every protein of the cell, and an exhaustive 

 enumeration of the end effects might well include every structure and 

 function of the organism. In such a case, the secondary damage can 

 be prevented by supplying the deficient amino acid. Therefore, the 

 sole function of the gene in this case is to play some essential role in 

 the synthesis of an amino acid. Actually, this role is restricted to a 

 single step in the synthesis: a single reaction is abolished in the mu- 

 tant, while all others proceed normally. The assumption follows that 

 the gene plays a role in the synthesis of the enzyme which catalyzes 

 the reaction. 



It seems to me that this argumentation is essentially the same as 

 our old physiological theory of heredity ( 1916c, 1920a, 1927 ) with the 

 addition only that the product catalyzed by the gene is always first an 

 enzyme for a single synthetic step. In my theory the accent was on 

 the kinetics of the primary reactions, in order to explain their time 

 interaction, the "network" of interaction; here the accent is upon the 



