THE NATURE OF THE GENE 303 



the changes of the centers, which are arranged after the model 

 of steps. The facts were given upon which this concept was 

 based, namely, the behavior of the scute alleles. But it is 

 known that other series of multiple alleles do not exhibit compar- 

 able phenotypic effects. In the chapter on multiple allelomorphs, 

 we considered those cases in which manifold effects of multiple 

 alleles seemed to behave rather independently of each other. 

 Friesen (1931), who analyzed one such ease, thinks that they must 

 be explained (also the scute case) by the assumption that a single 

 gene never mutates but always a more or less long chain of genes. 

 He speaks of chain mutations, which he believes to be the 

 prototype of mutations. This idea, which it would be difficult 

 to prove, is in principle not different from the subgene concept. 

 In both hypotheses, actual or apparent difficulties in explaining 

 phenotypic effects as due to a single gene-controlled process are 

 surmounted by projecting a corresponding multiplicity into the 

 germ plasm. The subgene theory does it by subdividing the 

 gene; the hypergene theory, as we might call it, does the same by 

 assuming a change in a chain of genes. The same criticism (see 

 page 296) applies therefore to both conceptions. The theory 

 has, however, the significance of showing the growing need of 

 considering the gene only as a part and not as a unit. Friesen 

 actually says that the assumption that genes are united into 

 groups means that they are not independent physicochemical 

 structures but that, in spite of a certain independence, they show 

 some structural interrelations. The same statement may also 

 be found in Brink's work (1932). He concludes from the facts 

 relating to translocations in maize that the chromosome consists 

 of groups of physiologically interdependent genes. Therefore, 

 the propinquity of the genes within a group is essential to normal 

 gene action in a general physiological sense. 



6. OUTLOOK UPON THE THEORY OF THE GENE OF TOMORROW" 



We have mentioned a number of facts that point in the direc- 

 tion of a conception of the gene more as a part of a higher unit 

 than as an independent one. The developments in the last years 

 of genetical research have now led to a point where it has become 

 necessary to ask the radical question : Is not the whole conception 

 of the gene as a hereditary unit obsolete? The facts that make 



