Computerized densitometry of Feulgen-stained CHO cells was used to collect data on micronucleus DNA content as a function of radiation dose. A cytochalasin-B block technique was used to assess the DNA content of each micronucleus relative to the DNA in its own binucleated cell. Distributions were compiled on the number, percentage of cellular DNA per micronucleus, and total DNA loss to micronuclei per individual micronucleated cell as a function of dose. Nonparametric distribution summaries were used to compare response distributions as a function of dose. Mean micronucleus DNA content did not vary significantly with dose. A dose-dependent increase was noted in the fraction of micronucleated cells, the average number of micronuclei per micronucleated cell, and the percentage of total DNA in micronuclei per micronucleated cell. The data on percentage of cell DNA per micronucleus appear sufficiently detailed to be useful for studying mechanisms of chromosome fragment segregation and fusion during micronucleus formation.

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