Medical Genetics Gamma and X-Rays These can act directly on DNA however, most damage is caused indirectly when molecules around the DNA such as water are ionized creating free-radicals, substances With unpaired electronsMedical Genetics Gamma and X-Rays These can act directly on DNA; however, most damage is caused indirectly when molecules around the DNA such as water, are ionized, creating free-radicals, substances with unpaired electrons