266 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1953 



of the thousands of linearly arranged entities which form the chromo- 

 somal gene string. We do not know whether the molecular analysis 

 of the chromosomes will lead to the discovery of clearly separate spe- 

 cific entities, linearly arranged, and insulated from each other by less 

 specific material. An alternative has been suggested, according to 

 which a whole chromosome may be a unified kind of super-macro- 

 molecule, and the genes only regions of specific chemical activity of 

 parts of the whole. In this extreme form the alternative is not likely 

 to be correct, since it is possible in the living cell to break a chromo- 

 some at many places and still retain the functioning of its parts. 

 Interestingly enough, though, this functioning often is slightly altered 

 from its normal action in the unbroken chromosome. There is some 

 interrelation of neighboring genes, be it interpreted as interaction of 

 separate molecular units or as interdependence of subunits of a larger 

 molecular aggregation. 



Wliat started as a problem of passive transmission has become a 

 problem of active functioning. Cell growth and development are 

 now known to be founded on genie action. A simple experiment made 

 75 years ago, of cutting an ameba into two parts, one with the 

 nucleus and the other without it, had shown the necessity of the 

 nucleus for continued life and growth. Now the geneticist can show 

 that the loss of a single gene may lead to damage and death. This 

 new fact has provided a new tool to the experimenter. While it 

 seemed hopeless to replace from the outside the activities of a whole 

 nucleus, it became possible to discover the specific cause of trouble 

 due to lack of a single gene, and to supplement the cell or the many- 

 celled organism with a compomid which it had lost the power to 

 manufacture itself. Not that one can give such a cell a new gene, 

 but at least we can supply a necessary product that is otherwise 

 gene-dependent. And what is possible for one lost gene is possible 

 for two and more. We do not yet know how much of the intrinsic 

 groundwork of an organism we can do without as long as we take 

 over its jobs. That one can go very far in this substitution is not 

 a discovery of man's intellect. All through the evolution of life 

 many forms have degenerated, losing their relative autonomy and 

 becoming dependent parasites upon other creatures. 



The role of the genes as key reagents in the biochemistry of the 

 cell is being elucidated by the brilliant work of our contemporary 

 biochemical geneticists. They have clarified many of the steps in 

 which the genes take part in the synthesis of amino acids, vitamins, 

 and other essential compounds. Different genes control or participate 

 in successive steps in the so-called biosynthetic pathways. These 

 studies have made genetics a central aspect of the science of cellular 

 physiology which comprises nutrition and growth, energy transfer in 



