Analysis of chromatid segregation in CHO cells at mitosis

In the present paper the results of an analysis performed at h13 on chromatid segregation that occurred at hl2 in CHO cells treated and untreated with K&O, are presented. The percentage of li& chromosomes (BB x BB chromatid pairs) in a cell at h13 has been estimated and the empirical frequency distributions of light chromosomes in the different experimental groups have been compared with the theoretical ones (sums of binomial distributions with p=0.5) by means of the non-parametric Kolmogorov-Smirnov test. In all cases a significant difference has been found, together with a shift to the “left” (i.e. pCO.5) of the maximal frequency classes. This behaviour has been explained by assuming the existence of a selective mortality factor acting on cells with light chromosomes prevailing. This cellular mortality of light cells has been attributed by some authors to the presence of the younger one of the two parental DNA strands collecting the damages which occurred during the previous generation. On the contrary cells with dark chromosomes prevailing (BTx BB pairs) yield DNA molecules with the older parental strand and do not collect the damages from the previous generation, and in consequence are not submitted to the action of the selective factor. Further, the greater shift leftward registered in the groups of cells treated with chromium has been explained by assuming