470 GENETICS OF SOMATIC CELLS 



situ, 1309 tissue-culture derivatives, 600 and ascites tumor cells. 840, 783 Attention had 

 been directed earlier by German workers to the last type of cell as a potent experimental 

 tissue. In the interim, a number of alterations in technique, particularly those 

 regarding hypotonicity, 607, 609 led other workers to rally to the challenge of adapting 

 meiotic and mitotic mammalian cells to the current array of experimental approaches. 

 Since the early 1950's, an ever-increasing number of participants have considered the 

 prospects of utilizing chromosomal cytology as a tool to evaluate factors affecting 

 cellular viability, mutagenicity, transplantability, and numerous physiologic and bio- 

 chemical expressions. Evidence that a large number of human syndromes are associ- 

 ated with cytogenetic abnormalities has been developed in a remarkably brief period, 

 and recent studies on mammals have yielded an increasing assembly of heritable 

 patterns among rodents which provide ideal counterparts of syndromes clinically 

 important. 190 ' 613, 866, 1097, 1280 An equally promising area has been opened as a 

 result of the over-all advances in tissue culture. There is every reason to believe that 

 the coming decade will continue to foster fertile premises for developments in the 

 approaches that apply to genetics of somatic cells, with greater emphasis being given to 

 controlling components of the environment. 312, 330, 895, 941, 1027, 1088, 1359 Increasing 

 use of trials in vitro as compared to those in vivo is primarily due to the esthetic qualities 

 of the former system with the possible simplification and/or control of environmental 

 factors. Nevertheless, a satisfactory outcome of effectively planned studies in vitro 

 will depend largely on ability to synthesize genetically controlled living sources from 

 which to isolate the appropriate types of cells. If long-term cultures of blast-like 

 precursors are readily obtained, the shift toward analyses in vitro will be hastened. 

 Although the trend today is toward subcellular levels of study, cytogenetic methods for 

 cells in vivo must be available to simplify further and to evaluate pleiotropic expressions 

 of a given mutation when cells are placed in vitro. 



Future immunogenetic approaches employing normal lymphoid or reticuloendo- 

 thelial derivatives in vitro require cautious attention. Isolation of these desirable types 

 of cells is more worthy of trial than the use of some of the present types of unknown 

 species and sex. Invariably, continuous propagation of cells features numerous 

 chromosomes, some or many of which may be entirely new structurally and reflect 

 properties that would have failed to survive during the course of selective evolutionary 

 processing of cytogenetic mechanisms. 



Physical and chemical measurements of any type of cell are certain to reflect the 

 degree of variegation that characterizes the cellular population. In the event that a 

 type of cell is chromosomally stable, that is, displays extremely low frequency of 

 chromosomal breakage and/or a limited variation in chromosomal distribution (aneu- 

 ploidy), it is usually assumed that the frequency of genie or point mutations is equally 

 limited. On the other hand, fluctuating chromosomal numbers and forms will lead 

 to innumerable variants, especially when numerous sublines are distributed to other 

 laboratories. Among a few of the prime requisites for the study of somatic cells in 

 vitro are stability or orderliness of the karyotype (number and form of chromosomes) , 



