4,98 GENETICS OF SOMATIC CELLS 



9. Distinct susceptibilities and resistance to viral agents. 



10. Viability unimpaired by routine freezing procedures. 



1 1 . Pleiotropic expressions of metabolic mutations. 



Ideal types of cells may be either normal or malignant in origin. The latter form 

 will provide the opportunity to involve additional selective pressures during the course 

 of alternative trials in vitro and in vivo. As expected, ideal types are exceedingly rare in 

 occurrence and certainly very limited in distribution and application at the present 

 time. Puck, Ciecura, and Robinson 1028 reported their procedures as being most 

 satisfactory in providing rapidly proliferating lines of human cells bearing 46 chromo- 

 somes and cells from the opossum with 22 chromosomes. Since their tissues are 

 heterozygous and reproduction of the opossum most difficult to manage under domesti- 

 cation, the observed constancy of chromosomal number only partially meets require- 

 ments necessary for a system in vitro to be repeated effectively at the convenience of the 

 investigator. 



A rigid pattern of constancy in chromosome number may not necessarily be suited 

 for experimental in-vitro genetics when new lines of cells with specific chromosomal de- 

 letions are desirable. Currently monosomaty of an autosome and nullisomaty of the 

 X 2 or Y chromosomes (XO) are available in some strains of cells from the Chinese 

 hamster. 1463, 1464 In the future, if disjunction can be controlled, a larger variety of 

 viable monosomies and trisomies may be synthesized and subsequently isolated by 

 cloning procedures. In our hands, chromosomal imbalances are characterized by 

 alterations in the gross appearance of the cells, affinity for glass, plating efficiency, 

 attraction or repulsion of neighboring cells, and the like. The presence or absence 

 of visible X chromosomes also influences colonial appearance and transplantability in 

 vivo. li63 - 1464 Many of the above features noted in cultures of cells from the Chinese 

 hamster are less easily recognized in other species which are also near-tetraploids. 

 Clonal appearance is not well correlated with chromosomal ratios after extended propa- 

 gation of cells. 



The influence of chromosomes on gross anatomy and on primary and secondary 

 sex characteristics is evident in most striking fashion among disturbed human somato- 

 types. A bit more limited in expressiveness are the autosomal relationships that tend 

 to result in Mongoloid-like expressions. The altered monosomic or trisomic fibroblast 

 derivative is certain to reflect pleiotropic (biochemical) expressions in the in-vitro 

 environment, even though the intact soma provides greater resources and substrate to 

 complete defective metabolic pathways. 



PROPERTIES OF THE CHINESE HAMSTER 



Cytologic characteristics 



1. Low chromosomal number of 10 readily recognizable autosomal pairs. 



2. An X X X 2 Y or triheterosomic somatic sex expression. 



