270 Action of the Genetic Material 



eflFect in terms of corpuscular genes, as well as of a number of phe- 

 nomena of genie action. We have considered some of these problems 

 (see I 3 C c ee ccc), and letum to them now exclusively from the 

 point of view of primary genie action. 



Muller as well as OflFerman (1935) at first suggested (since 

 abandoned by Muller) that position effect is caused by a gene acting 

 in a different neighborhood. This would mean that the primary gene 

 products react directly at the chromosomal surface with those of other 

 genes and especially with those of adjacent genes. Therefore a 

 changed gene neighborhood would interfere with these reactions. This 

 idea does not work, for many reasons. As we discussed in detail before, 

 the position effect makes a "gene" act as if it had mutated, though we 

 had to qualify this simple description ( I 3 C c cc ). If this is due to an 

 abnormal neighborhood, it would mean that an intact gene cannot be 

 affected except in one direction, namely, its typical mutant action. 

 Whatever neighboring material has got away from it or whatever 

 distant material has come near to it, whenever there is an effect it is 

 always the same (with a little variation within essentially the same 

 effect). This would mean an obligate all-or-none effect in the function 

 of the gene, whatever change occurred in the neighborhood. Logically, 

 this could not be distinguished from a gene mutation. This idea has 

 not much to recommend it, and has been abandoned by all but the 

 strictest believers in the classic gene. 



A recent revival of the general idea in a more modern form goes 

 back to some suggestions by Sewall Wright. Stern's explanation of 

 genie action (see Stern et ah, 1943-1946) was formulated in order to 

 solve the great difficulties of a consistent explanation of his dosage 

 experiments. He assumed that the gene has two independent at- 

 tributes, namely, its combining power with a substrate, and the ef- 

 ficiency with which the substrate is converted into gene product. 

 Thus access to the substrate is linked with the proper elaboration of 

 the gene products. More details will be given in the chapter on dosage 

 effects. For our present discussion the theory involves a gene at its 

 locus, a substrate which must be localized at the chromosomal surface 

 and must be different from point to point, in order to be used for an 

 explanation of position effect, and gene products which may or may 

 not be localized. 



From another point of view, involving the idea of position effect 

 in a different sense, the problem of primary genie reactions in situ 

 (chromosomal) has come up in the work on so-called pseudoallelism 

 discussed previously (I S C c ee ccc). Pontecorvo (1952a) started 



