Relationship between the ratio of parental chromosomes and parental doubling times in chinese hamster‐mouse somatic cell hybrids

Somatic hybrids obtained by the selective method of Littlefield between a permanent line of Chinese hamster cells (Wg3) and one of mouse cells (3TP) showed a preponderance of biarmed (hamster) chromosomes. Under normal culture conditions (37°) the doubling time of the parental mouse cells was twice as long as that of the parental hamster cells. If the temperature of incubation was lowered (31°), the relative difference in doubling times was reduced; in hybrid lines obtained under these conditions, the proportion of biarmed chromosomes was also reduced. Upon extended cultivation the average number of telocentric chromosomes progressively decreased in all hybrid lines tested, regardless whether these were started and maintained at 37° or at 31°. An inverse correlation was observed in hybrid cells between doubling time and relative proportion of biarmed chromosomes, suggesting that the karyotypic changes observed after extended culture were due to the selective overgrowth of cells with a high biarmed to telocentric ratio.