274 Action of the Genetic Material 



( 1952 ) . It turned out that the well-known multiple alleles apricot and 

 white are pseudoalleles in Lewis' sense, each with its own series of 

 other alleles, the order being apr-w. Again, the explanation of the 

 so-called position eflFect (wild type in coupling, pinkish in repulsion) 

 is that the mutant gene apr impairs the functioning of w+ or that w 

 impairs that for apr+. Thus one of the genes controls a step A-> B 

 and the other a step B -> C in a biochemical reaction chain A — > B 

 -^ C. The "position effect," then, results from the failure of substance 

 B to diffuse from one chromosome to the other; the reaction chains 

 in the two homologues are carried out independently of each other. 

 For our present discussion these interpretations contribute the as- 

 sumption of primary gene products acting in situ, further competition 

 of the products for a substrate, and a sequential order of this reaction, 

 which is the new addition. The details, it is clear, are worked out so 

 as to fit the principle of the classic gene and the origin of pseudoalleles 

 by duplication of genes with subsequent small changes in function. 

 But the basic postulate is the same as that discussed in Pontecorvo's 

 case, and so are the objections. 



Lewis applies further the idea of the sequential reactions to an 

 explanation of the phenotypic relations in different bithorax alleles. 

 For our present discussion the details of the hypothesis are not 

 relevant, except that they are an expression of the belief that the 

 primary gene products in situ already take part in reactions which 

 decide the trends of all subsequent phenotypic development. There 

 is no reason to assume that the action of genie material in so-called 

 pseudoallelic series differs basically from that of other genie material; 

 hence it would follow that all genie actions are initiated by reactions 

 in situ between the primary genie products. Since the whole idea 

 works only with millimicromolecular, not diffusible, substances, it is 

 difficult to beheve that this is typical for all genie actions. The entire 

 hypothesis is based upon the unproved premises mentioned above. 

 Thus I cannot believe that it has yet been proved that primary genie 

 products start their decisive reactions at the chromosomal site. We 

 shall return to the problem of the primary products and the chro- 

 mosomal site when discussing polyteny in relation to differentiation. 



Altogether, we may say that in spite of a good deal of clever 

 hypothesizing, we are still completely in the dark about what happens 

 at the genie sites of the chromosomes when genie action produces the 

 first reactive genie products. We do not know what the primary 

 products are, how they are produced by the genie material, how and 

 with what they react, where the reactions take place, and what the 



