Evidence for the recessive nature of cellular immortality.

Fusion of immortal cell lines with normal human fibroblasts or certain other immortal cell lines yields hybrids having limited division potential. Cellular immortality was found to be a recessive phenotype in hybrids. It was also found that at least two separate events in the normal cell genome can result in immortality. In fusions involving certain immortal parent cells, these events can be complemented to result in hybrids with finite division capacity.