George Klein, M.D. 



GENETICS of SOMATIC CELLSt 



Originally, the study of heredity was mainly concerned with the ways and means 

 by which genetic information is transmitted through the germ cells of higher organisms; 

 and sexual crossing was the predominant, if not exclusive, method of approach on 

 which all important concepts were based. The first important change in this situation 

 came with the development of microbial and, particularly, bacterial genetics. Initially, 

 bacteria were believed to multiply exclusively by binary fission and to lack every form 

 of sexual reproduction. Nevertheless, consistent attempts were made to apply the 

 concepts derived from the genetics of higher organisms to the study of bacterial heredity, 

 but this met with considerable skepticism in the beginning. From the viewpoint of the 

 geneticist, the approach often seemed too indirect and uncertain, particularly since it 

 was impossible to distinguish between genotype and phenotype, as there was no method 

 available by which hybridization or other forms of intercellular genetic transfer could 

 have been accomplished. Microbiologists who were not thoroughly acquainted with 

 genetics were not ready to accept the view that the same basic laws may apply to bacteria 

 as to higher organisms and both may contain essentially the same type of genetic 

 material, organized in a similar fashion. Variation in bacteria was often interpreted 

 as developmental rather than genetic. Superficial consideration of the many adaptive 

 phenomena occurring in bacterial populations after exposure to various noxious agents, 

 such as chemicals, antisera, bacterial viruses, and the like, has led to the view that the 

 heredity of lower organisms may be more easily influenced by the environment than 



f The work of the author and his collaborators quoted in this paper has been supported 

 by the Swedish Cancer Society, by grants C-3700 and C-4747 from the National Cancer 

 Institute, U.S. Public Health Service, and by the Knut and Alice Wallenberg Foundation. 



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