Table 1.

Major Sources of DNA Damage

Sources of DNA damage	Nature of the damage
Radiation
UV	ssb
Ionizing radiation (x-ray, γ-rays)	dsb and ssb
Chemicals
Alkylating agents	ss damage
Bleomycin and oxidative free radicals	dsb and ssb
Replication errors	ss mismatches, deletions, and insertions
Endogenous DNA enzyme errors
V(D)J recombination	ssb and dsb
Class switch recombination	dsb
Other enzymes	ssb and dsb

ssb, single-strand break; dsb, double-strand break.