Which type of DNA damage is most commonly produced by ionizing radiation?

• A. Double-strand breaks
• B. Small base-pair lesions
• C. Single-strand breaks
• D. A combination equally distributed

Answer: (B)

Ionizing radiation mainly causes DNA damage through indirect effects from water radiolysis, which generates reactive hydroxyl radicals that attack the DNA. These radicals most often modify the nucleobases themselves, creating small base-pair lesions and abasic sites rather than immediately breaking the backbone. Although single-strand breaks occur, and double-strand breaks can result when two lesions are close on opposite strands, base damage is the most frequent initial lesion produced. Double-strand breaks are relatively rare but highly destructive when they occur, which is why they’re associated with severe consequences even though they’re not the most common outcome. So, the typical, most common type of DNA damage from ionizing radiation is base-pair lesions due to direct base modification by radical attack.