Mammalian Chromosomes in Vitro. IX. On Genetic Polymorphism in Cell Populations2

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Abstract
Five cell strains MC3, CF1-C-9, NCTC 2071 (NCTC clone 929, strain L), L-P55, and L-P55-N2, all of murine origin, were studied with respect to their chromosomal constitution. The last 3 strains were sublines of NCTC clone 929 (strain L). All of them were heteroploid. Besides the changes in chromosome number, each strain possessed from 10 to 20 metacentrics and a few subtelocentric chromosomes. Each strain had its characteristic karyotype and was cytologically identifiable. Cells of strains L-P55 and L-P55-N2 contained 1 or 2 long dicentric chromosomes. However, a small proportion of the cells in strain L-P55 was void of this element. This dicentric chromosome was probably identical to the dicentric that occurred frequently in strain L2 established by Fedoroff in Saskatoon, Canada. Within each strain considerable variations of chromosome number as well as combination of chromosome types were recorded. Therefore, each strain is heterogeneous in its genetic make-up. Genetic polymorphism conceivably prevails also in populations of other cell strains. It provides different genotypes for the populations to adjust themselves to various adverse selection forces that may be applied to them.