Mammalian Chromosomes In Vitro. XIV. Genotypic Replacement in Cell Populations2

Abstract

In the 1958 sample, cells of strain L-M (a subline of strain L carried in the Ann Arbor, Mich., laboratory) possessed 2 marker chromosomes, the D and T. The D chromosome was a large, subtelocentric chromosome whose long arm could be subdivided into 4 segments by 3 secondary constrictions, the last constriction being most conspicuous. The T chromosome was probably an isochromosomal derivative of the former. In the 1960 sample of the same strain, those 2 markers disappeared from the stem line. The stem cells contained 2 new marker chromosomes: the E, a chromosome similar in shape to D, but with the long arm having only 3 segments, and the F, a subtelocentric with a very short, knoblike second arm. The long arm of F was identical to that of D in morphological characteristics. New genomes are constantly generated in cell populations in vitro. Some of the new genomes, with adaptional advantages or superior growth capacity, may replace the original stem line. Special marker chromosomes may enable investigators to identify the origin of some particular sublines.