Phenotype of low proliferative potential is dominant in hybrids of normal human fibroblasts

A biochemical selection system was used to isolate hybrids after fusion of human diploid fibroblast clones of varying proliferative potential. The distribution of proliferative potentials of the hybrids resembled that of the parent with smaller proliferative potential. Therefore, the phenotype of limited division was dominant in hybrids. This dominance was associated with cells that could achieve seven or less divisions present in the parent populations. Terminally nondividing cells present in clones near the end of their proliferative potential differed from those present in clones that had ceased division (senescent), in that a higher percentage could be induced to divide at least once following fusion with a cell capable of division.