How can ultraviolet radiation and X-rays increase the rate of mutation?

Ultraviolet (UV) radiation and X-rays increase the rate of mutation by directly damaging DNA or creating reactive chemical species that alter its structure, often overwhelming the cell's DNA repair mechanisms.12

Ultraviolet (UV) Radiation

UV light acts on DNA primarily by causing the covalent linking of adjacent pyrimidine bases, a process known as pyrimidine dimerization. These dimers create physical distortions that block normal DNA replication. Additionally, UV radiation can induce photosensitization, where energy is transferred to molecular oxygen to create reactive "singlet oxygen" that attacks cellular components, including DNA.31

X-rays (Ionizing Radiation)

As a form of ionizing radiation, X-rays damage DNA through two main pathways:
* Direct Damage: High-energy radiation can break both strands of the DNA molecule, leading to chromosome breaks, deletions, or translocations.4
* Indirect Damage: Ionizing radiation creates free radicals within the cell, which oxidize DNA bases—most notably guanine—leading to mutations such as G-T transversions.12

If these lesions are not corrected by repair enzymes, or if the cell attempts to replicate over the damage using error-prone pathways, the alterations become fixed as permanent mutations.12