Cellular senescence, the terminal nondividing state that normal cells enter following completion of their proliferative potential, is the dominant phenotype in hybrids of normal and immortal cells. Fusions of immortal human cell lines with each other have led to their assignment to 1 of several complementation groups. MORF4 is a gene on chromosome 4 that induces a senescent-like phenotype in cell lines assigned to complementation group B.(supplied by OMIM).