THE GENE AND BIOCHEMISTRY 



complex self-duplicating unit than to modify it so as to give it a new 

 and useful property without sacrificing its power of self-duplication. 

 The first self-duplicating unit must have evolved from nonliving matter 

 at some time, and more complex forms must have evolved from it — 

 the alternative is some form of special creation. There would seem 

 to be less difficulty in imagining a primitive "protogene" mutating to a 

 true gene with a heterocatalytic property than its spontaneous origin 

 in the first place, even if, as Oparin (33) supposes, it arose in a world 

 containing preformed organic molecules of many kinds. Nor is there 

 any apparent reason why such protogenes could not nmtate in many 

 diflferent directions in order to give rise to many different organic 

 catalysts. In present-day cellular organisms there exists a possible 

 mechanism for acquiring totally new reactions. Occasionally, through 

 accident, one or more genes become duplicated, i. e., a small segment 

 of a chromosome occurs twice in every set. The duplicated genes 

 will be unnecessary to the organism and will be expected to disappear 

 through loss mutations, since such mutations are not disadvantageous. 

 But such a duplicate gene may occasionally undergo mutation in such 

 a way that it directs the formation of an entirely new enzyme. If this 

 new enzyme should happen to catalyze a reaction that improved the 

 organism in competition with its relatives, the new reaction would be 

 retained. Such new reactions might add new compounds or they 

 might bring about the reverse of the specialization process, which leads 

 in the direction of parasitism. In this way, as Horowitz (20a) has 

 pointed out, the first primitive organisms might gradually have built 

 up systems of synthesis which freed them of their dependence on 

 preformed organic molecules originally present in the environment. 



Through such advances as hav-e been indicated we appear to 

 be moving rapidly in the direction of a better understanding of what 

 genes are and what they do. We are no longer content with a knowl- 

 edge of the laws by which they are transmitted from one generation 

 to the next. We see that they are basic functional units of the organism 

 and that, by taking advantage of their tendency to mutate, we can use 

 them as powerful tools in determining the course of biosynthesis and 

 in imderstanding other aspects of metabolism. Their relations to 

 enzymes and antigens are becoming known. Precisely how they 

 function in duplicating themselves and in directing the specificities of 

 proteins, nucleic acids, and possibly other large molecules is a question 



