Acute Radiation Response of Mice from a Cross between Radiosensitive and Radioresistant Strains.

HE existence of genetic differences in the radiosensitivity of inbred mouse T strains has been well established under controlled experimental conditions (KOHN and KALLMAN 1956; GRAHN and HAMILTON 1957). These studies have indicated that strain BALB/c is the most radiosensitive of those investigated and that strain C57BL is relatively resistant. As a consequence of this known difference, strains BALB/c and C57BL were selected for a study designed to give information on the mode of inheritance of radiosensitivity. In toxicity testing, observed sensitivity is assumed to be a continuously distributed variable (MATHER 1946). When rectified, this distribution is described by the dosage-mortality slope-the latter being inversely proportional to the standard deviation of the distribution. The mean or median of the distribution (LD,,) and a measure of dispersion (the dosage-mortality slope) will be used in this study to describe the acute lethal response. The slope has previously been employed in the estimation of phenotypic variances for inbred strains ( GRAHN and HAMILTON 1957) and should provide, for segregating generations, a means of estimating the genetic variance.