GENES IN CONTROL 37 



supported by the reality of a visual picture all the way up to 

 and including the germ cells of man. 



The gene, as has been mentioned, is a giant nucleoprotein 

 molecule of extreme complexity. Although it is ultramicro- 

 scopic in size, it has probably been seen recently by investi- 

 gators using the electron microscope; and there are situa- 

 tions in nature, notably the giant chromosomes of certain 

 glands in flies, where ordinary microscopy indicates the 

 position of the gene. It is fundamentally a long-chain mole- 

 cule, probably in extended form, and the chemist now has 

 some idea of its structure. It is apparent that the duplication 

 of a given gene, it being so enormously complex, could 

 hardly be expected to be forever perfectly accomplished 

 each time the gene divides. Almost any change that occurs 

 would alter the way in which the gene acts on the organism. 

 This, possibly, is the manner in which mutations are pro- 

 duced although we cannot as yet be sure. We do know that 

 outside influence, like cosmic rays, X rays, heat, chemicals, 

 etc., although effective in increasing the rate of gene muta- 

 tion, are apparently not the primary cause. And we also 

 know that although we often use the word "random" in re- 

 ferring to these changes, they are, of course, limited to the 

 possibilities of a particular gene's chemical configuration. 



These mutations, however they may be brought about, 

 are effective in ultimately changing the structural, physio- 

 logical, and behavioral pattern of the organism. Changes 

 may be beneficial or definitely harmful, even lethal, or they 

 may be quite valueless adaptively. A mutation may occur 

 which, although of no particular value at the moment, is 

 later very useful when environmental factors change; and 

 the unhappy converse can also be true. These are pre-adap- 

 tational mutations. Organisms with sufficiently flexible 

 genes, or with useful pre-adaptational mutations already in 

 their make-up, have been the successful forms when the 

 restless environment changed. Through the mutational 

 changes which are occurring within the organism and the 



