Preface 



Genetics is the core science of biology. Its ultimate subject matter is a 

 class of chemical compounds, the hereditary determinants, which are the 

 prime movers of cellular metabolism and, thereby, of the even more com- 

 plex processes of development and evolution. 



Historically, genetics began with the demonstration of genes which be- 

 haved as unit factors in sexual transmission in higher plants and animals. 

 Subsequently, in a great burst of fruitful research, genetics became estab- 

 lished as a predictive science dealing with the organization and behavior 

 of hereditary material at the biological level. Genetics is unique in biol- 

 ogy for its broad and fundamental theory, and for methods which provide 

 approximate solutions of the problems posed. In the 1930' s it was already 

 possible to build upon the theory of genetics, for example, in the experi- 

 mental study of evolution, in the analysis of genetic effects upon physiol- 

 ogy and development, and in application to plant and animal breeding. 



Today, the science of genetics is coming to grips with the analysis of 

 heredity at the molecular level in studies of the hereditary determinants: 

 their chemistry, the molecular basis of their replication, mutation, and 

 transmission, and the translation systems by means of which they exert 

 their control over all cellular processes. 



Progress in molecular genetics began to accelerate following the intro- 

 duction of microorganisms into genetic research, a development which has 

 been gaining momentum steadily since about 1940. In the last 20 years, 

 there have been tremendous advances in this field, and in its impact upon 

 other areas of biology. With microorganisms it has been possible to per- 

 form certain decisive experiments, technically infeasible with higher 

 organisms, which have clarified and solidified points of genetic theory 

 previously the subject of speculation. At the same time, some wholly un- 



