446" GENETICS OF SOMATIC CELLS 



cell tumors which can be expected to lend themselves excellently to the isolation of 

 single-cell clones in vivo,* 15 - 532 may become important tools for the study of such prob- 

 lems as the ability of a single cell to produce two different specific proteins at the same 

 time, and the mutability of product specificity in untreated cells and after exposure to 

 X rays and various mutagenic agents. In the words of Burnet: 149 "The multiple 

 myeloma findings provide the best possible material for displaying the salient features 

 of the clonal selection approach to the phenomena of antibody production and malig- 

 nancy. The globulins produced in multiple myelomatosis are abnormal but they 

 remain consistently of the one physical and chemical pattern which has been, as it 

 were, chosen from a probably unlimited number of possibilities. This constancy of 

 pattern can hardly be interpreted in any other fashion than as a genetically controlled 

 quality of the clone." 



The findings on the plasma-cell tumors represent another example of the individual 

 distinctiveness of different neoplasms of closely similar origin, already indicated by the 

 previously discussed facts regarding the individual antigenicity of methycholanthrene- 

 induced sarcomas and certain lymphomas in their autochthonous or isologous hosts. 

 Such an individuality is also suggested by the majority of studies on chromosomes. 

 Since the latter subject is discussed by Dr. Yerganian in another chapter, it will not be 

 reviewed here in detail. It may be pertinent to mention some points, however, with 

 regard to chromosomal studies that appear to be relevant for the present discussion. 



Chromosomal markers are especially useful to establish the identity of cell lines 

 and to reveal possible contaminations. 1076 ' 1319 They are also valuable for the study 

 of genetic variation in populations of tumor cells and, when combined with the experi- 

 mental isolation of single-cell clones, 532, 841 they can yield information about such 

 problems as the ability of the various karyotypes to become established as clones, the 

 relationships between biological and chromosomal variation, and the speed with 

 which morphologically detectable chromosomal variation is being reestablished within 

 the originally homogeneous population of a clone. Since cells of different chromosomal 

 constitutions can display different sensitivities to the homograft reaction within the same 

 tumor-cell population, 531, 533, 690 it is possible, in favorable cases, to establish tumor 

 sublines, differing in their modal chromosome number, by immunoselection from the 

 same neoplasm. 531, 690 These can be used as tools for studies on the relationships 

 between number of chromosomes and various biological characteristics. Such com- 

 parisons are more rigorous and reliable than conventional studies on unrelated tumors 

 differing in numbers of chromosomes and many other additional characteristics. 

 Comparisons of this type have been carried out with regard to parameters of growth 530 

 and radiosensitivity, 1052 and they have revealed information that was not available 

 from previous analogous studies on unrelated tumor lines. 



Viral tumors and infective heredity. — Recent advances in virology and particularly 

 in bacterial and phage genetics have tended to bridge the conceptual gap between 

 mutation and viral infection, and it is now a matter of taste whether to consider bac- 

 teriophages as genes that function at the parasitic level or as parasitism at the genetic 



