When cells are irradiated with ionizing radiation, one of the readily observed effects is the production of chromosome aberrations. These aberrations of the genetic apparatus can lead to drastic effects on cell division and cell survival. Different types and amounts of aberrations are induced at different stages of the cell cycle according to the submicroscopic organization of the chromosomes and nuclei within the stages. Thus at prophase each chromatid acts as though double in its response to radiation, whereas later, after the chromatid has become a daughter chromosome and entered G1 of the next cycle, it acts as though single. Such changes have profound implications for our understanding of chromosome structure. Aberrations that lead to anaphase bridges can prevent cytokinesis. Others that lead to genetic imbalance among the daughter cells can lead to lowered survival. It is not yet clear, however, how important this imbalance is in studies of cells in tissue culture, for these cells are grown in fairly complete media and can stand a large amount of polyploidy and aneuploidy.

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