THE NATURE OF THE GENE 4OI 



crossing-over and X-ray breakage. It is quite posssible that only a 

 small part of the gene defined in this way is actually active in the 

 control of development. We cannot rule out the possibiUty that this 

 activity is due to some particular group within the large protein-nucleic 

 acid complex we have been discussing. In fact, the small size of the 

 * 'sensitive volumes" found for particular steps of mutation might 

 suggest that only quite restricted regions are concerned in producing 

 the phenotypic differences between two allelomorphs; but we have 

 pointed out the many uncertainties in the interpretation of the sensitive 

 volume measurements. 



On the other hand, it is quite possible that all primary gene products 

 are enzymes and therefore probably proteins, which may be similar 

 in composition to the genes themselves. It would then be in order to 

 suggest a connection between gene activity, in which enzymes were 

 produced and Hberated into the cytoplasm, and gene reproduction, in 

 which similar bodies were formed but retained in the neighbourhood 

 to form a new chromosome. 



It will be apparent from the above discussion that the exact knowledge 

 at our disposal is so meagre that very many alternative hypotheses are 

 still possible as to the nature of the chromosome, and the gene in its 

 different senses. However, the enormously important effects of the 

 genes on development, their capacity for identical reproduction, and 

 the fact that they, rather than the cells of an earUer time, seem to be 

 the most ultimate units into which we can analyse Uving organisms, 

 make the problem of their constitution one of the most fundamental 

 questions of biochemistry, well worthy of discussion even long before 

 it can be fuUy answered. 



