Which statement about dose fractionation and genetic damage is supported by animal studies?

• A. Genetic mutational damage is more severe if a given dose is fractionated over years
• B. Genetic mutational damage is less severe if a dose is fractionated
• C. There is a clear threshold below which genetic damage does not occur
• D. There is no dose-response relationship for genetic damage

Answer: (A)

The key idea is how timing and repetition of radiation exposure affect heritable genetic damage. In animal studies, delivering the same total dose in fractions spread over years can lead to more germ cells acquiring mutations than a single, acute dose because germ cells are continually dividing and pass through stages where DNA repair is imperfect. Each fraction introduces new lesions, and between fractions some cells survive and continue to divide, potentially fixing unrepaired or misrepaired damage as heritable mutations. Over extended periods, multiple germ-cell development cycles mean more opportunities for mutations to be transmitted to offspring, so the overall genetic damage appears greater for fractionated dosing than for a one-shot exposure of the same total dose. The other statements don’t fit this observed pattern: there isn’t a simple threshold below which genetic damage is absent, and there is a dose-response relationship, with fractionation modifying the outcome in a way that can increase heritable effects in this context.