The Effect of In vitro Aging on Metaphase Chromosome Contraction in Human Lymphoid Cells

After differential staining of sister chromatids, ch romosome length distribution and averag~ ch romosome length were determined for human lymphoid cells in, respectively, the first, second, third, and fourth and later mitoses. A significant change in ch romosome length distr ibution and a marked decrease in average ch romosome length were found for cells in the four th and later mitoses. This supports previous suggestions that the observed changes in these parameters in cell popula t ion during in vitro aging are due solely to an increase o f cells in the fourth and later mitoses. chromatinizat ion of euchromat ic areas close to or placed within the major G band. The development of bromodeoxyur id ine (BUdR) staining technique for the morphologic differentiation of sister chromatids (Korenberg and Freelander, 1974; Latt, 1973; Perry and Wolf, 1974) has made it possible to differentiate between the first, second, third, and fourth and later mitoses (Tice et al., 1976). In this study, chromosomes 1 f rom human lymphoid cells in the first, second, third, and fourth and later mitoses were measured for comparat ive analysis of length distribution frequencies.