The application of lognormal frequency distributions (the logarithm of the original variate is distributed normally) in establishing the range of various nuclear parameters including interphase chromosome volume (ICV) and DNA per chromosome has been demonstrated for a large number of gymnosperm taxa (236 spp.). Parameters from the plot of the probit of cumulative frequency vs log ICV (based on lognormal distributions, and using the known correlations between ICV and acute and chronic whole-plant radiosensitivity) permit the prediction of the probable limits of radiosensitivity for all unsampled species for a given taxonomic group. Similarly, the range of predicted radiosensitivities for species having ICV's above or below any given value may be estimated from the plots, probit of cumulative frequency vs log ICV. The lognormal distributions of ICV and derived probable limits of acute and chronic LD50' s are given for many species of six gymnosperm families including the Pinaceae, Cupressaceae and Podocarpaceae, and separately for six genera of these families. General predictions of radiosensitivity are made for other gymnosperm families represented by fewer species. The feasibility of using the probit of cumulative frequency-log ICV approach is discussed with regard to the prediction of radiosensitivities on a broad scale in other taxonomic groups for which DNA per chromosome or ICV data are available.

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