X-RAY INDUCTION OF CHROMATID EXCHANGES IN MITOTIC AND G1 CHINESE HAMSTER CELLS PRETREATED WITH COLCEMID

Chinese hamster cells were synchronized by selecting mitotic cells from an asynchronous population, either with or without a 2-h pretreatment with Colcemid. In both cases, X-irradiation of mitotic cells induced 2 times as many chromosomal aberrations as irradiation of G1 cells. Without Colcemid pretreatment, 90 % of the exchanges induced in mitotic and G1 cells were of the chromosome type. Colcemid pretreatment did not affect the frequency of the chromosome type exchanges, but the treatment increased the total aberration frequency by a factor of 2-3 due to an increase in the frequency of deletions and the appearance of chromatid type exchanges (50 % of the total). The Colcemid effect is discussed in relation to a reduction in protoplasmic viscosity reported as a result of Colcemid binding to macromolecules. © 1969.