Chromosome Pulverization in Human Cells With Micronuclei2

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Abstract
A chromosome pulverization phenomenon observed in some members of the chromosome complement in human cells was studied. Autoradiographic examination revealed that pulverized chromosomes continued to synthesize their DNA, even after all the other chromosomes had completed synthesis. These abnormal chromosomes were considered to be derived from micronuclei, which were in many cells of the present cell line, and found to undergo an asynchronous DNA synthesis with the main nucleus. The incidence of interphasic cells having micronuclei corresponded well with that of metaphases with pulverized chromosomes. By coexisting with the main nucleus within the same cell, the late-synthesizing micronucleus may suffer from a disturbance in its performance of the normal process of chromosome condensation, leading eventually to pulverization at mitosis.