H-2 antigen variants in a cultured heterozygous mouse leukemia cell line. VI. Rate of emergence of the hemizygous variants and evidence that the variants preexist the selection.

The rates of emergence of H-2b- and H-2d- variants from an H-2b+/ H-2d+ heterozygous mouse leukemia cell line were determined by fluctuation analyses. The results show that the wild type cells throw off the H-2b- variants at about 10(-5) per cell per generation and the H-2d- variants at 10(-6) per cell per generation. The reason for this tenfold difference in the rates for the two symmetrical variants is not clear. The fluctuation analyses also indicate that the variants exist in the wild type population prior to exposure to the selective agents.