Non-interaction of Radiation-induced Chromosome Lesions inTradescantiaMicrospores

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Abstract
After a priming dose of 300 rads, a response curve for chromosome exchanges has been obtained at the time of minimal dose interaction. Compared with a single-exposure dose-response curve induced at the same time, the fractionated curve is displaced downwards, since there is no interaction at any dose combination. It also shows pronounced saturation at higher total doses, suggesting a reduction in the number of effective exchange sites available to the second dose. Further evidence for such a reduction comes from the observation that the observed yields are consistently below those expected on the basis of simple additivity of the yields from the two dose fractions. Assuming that the original population had a limited number of effective exchange sites, the loss of interaction is shown to be consistent with the repair of partially damaged sites, but the data do not exclude the possibility that dose-dependent site inactivation is also a contributing factor.