Gene Action 305 



have an early effect, such as genes for general growth, affect all 

 subsequent development ; other genes, such as the eye-color genes 

 in Drosophila, have an early differential effect and then no 

 longer exert any striking influence. 



In a recent symposium, Wright has made some interesting 

 suggestions regarding the physiology of genes. He has consid-. 

 ered especially the method by which a gene produces more genes, 

 the way it controls metabolism, and its behavior in connection 

 with the growth of an organism. 



We have previously pointed out that most geneticists believe 

 that a gene is produced by the reproduction of a preexisting gene, 

 which in some generally unexplained way produces another gene 

 like itself. Wright has shown that genes are not completely 

 autonomous but show a high degree of autonomy. He pointed 

 out also that a gene is a highly specific giant nucleoprotein and 

 that to consider that it might be built up in a step-by-step 

 fashion from very simple substances is to assume a very com- 

 plex process. He thought that it is more likely that within the 

 living cell various simple molecules from the nutrients that are 

 present are arranged on the surface of the gene in such a way 

 that the gene itself is duplicated (Fig. 85). 



Many cell processes occur as the result of the action of numer- 

 ous enzymes. Available information seems to indicate that these 

 enzymes are proteins, or proteins combined with a group known 

 as a prosthetic group, and generally obtained by the organism 

 from its food as a vitamin. It is generally believed, also, that 

 these enzymes are produced by gene action. A way they might 

 be produced has been suggested by Wright and is pictured in 

 the second section of Fig. 85. There is an obvious relationship 

 between the synthesis of enzymes and of new genes. 



Wright has also pointed out that certain phases of growth 

 involve the multiplication of proteins specific to the species and 

 to the individual. In this respect, growth is closely connected 

 with these other aspects of gene physiology that we have just 

 mentioned. If these proteins are produced in much the same 

 manner as the genes and enzymes just described, the problem 

 arises that the gene must have to produce millions of protein 

 molecules to account for a doubling of a cell, whereas each gene 

 produces only one daughter gene between these cell divisions. 

 This tremendous production of proteins must be accounted for. 



