G. W. BEADLE 



master molecules or models from which exact copies are made (11,18, 

 19,30,31,55). If this is so, their action may be visualized as one of 

 directing the construction of specific protein types plus whatever other 

 component parts genes may have. If the specificities of proteins 

 generally are copied from genes, the observed relations between genes 

 and enzymes and between genes and antigens should follow. For 

 every specific protein there should exist a gene carrying this same 

 protein. For every enzyme and antigen type there likewise should 

 be a gene. Because of a general tendency of mutation pressure to 

 eliminate genes that are of no advantage to the organisms, it might 

 be expected that for every protein type there would be only one corre- 

 sponding gene. The experimental evidence appears to support this 

 general interpretation, although it must be recognized that, in dealing 

 with genetic traits that can be described in terms of chemical reactions, 

 there may be an unavoidable selection of those cases in which gene 

 action is relatively simple. 



However proteins and other components of genes are synthesized 

 — whether by an orthodox stepwise mechanism or by some as yet un- 

 known mechanism by which many component parts are simultaneously 

 directed into their proper places by the master molecule (11) — the pre- 

 cursors of proteins, nucleic acids, and whatever other parts genes may 

 have, must be synthesized. Their synthesis will involve many enzymes 

 and a corresponding number of genes. Thus, before one gene can 

 determine the specificity of a new protein molecule, many other genes 

 must have acted. This amounts to saying that, in any multigenic 

 organism, the genes constitute a highly organized system, just as the 

 chemical reactions they direct are integrated in time and space in a 

 manner characteristic of a particular species. Furthermore, while a 

 particular gene will have only one primary action in determining 

 specificity of an enzyme or an antigen, the final physiological conse- 

 quences of a change in a single gene will be manifold. This can be 

 appreciated when one considers the consequences of depriving an 

 organism such as a rat of thiamin. The final consequence is of course 

 death, but before death occurs a series of changes of increasing com- 

 plexity take place. These can be brought about in the rat by remov- 

 ing thiamin from the diet. In the bread mold, which normally syn- 

 thesizes thiamin, the same end result can be effected as a result of an 

 analogous series of changes initiated by replacing a normal gene 



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