Does 9-azaguanine induce or select for chromosome number instability in human cell hybrids?

Segregant clones resistant to 8-Azaguanine (8AG) obtained from hybrids between clonal derivatives of the EUE line were analysed for chromosome number distribution. In almost all cases the 8AGR clones show chromosome losses and a greater variability in chromosome numbers than that of the parental hybrids and their non-selected subclones. A study of the karyotypic evolution of 8AGR segregant clones maintained for a prolonged period either in 8AG or in drug-free medium did not reveal any correlation between chromosome variability and the presence of 8AG. The preadaptive nature of the segregation to 8AG resistance is also indicated by the results of a fluctuation test.