Table 1.

Reasons and repair mechanisms of different DNA lesions.

Damaging agents	Replication errors	Ultraviolet light Chemicals	Ultraviolet light Alkylating agents	Oxygen radicals (ROS) Chemotherapeutics X-rays	Ionizing radiation Chemotherapeutics X-rays
DNA lesions	Base mismatch Deletions Insertions	Bulky adducts Intrastrand Crosslinks	Small adducts Reverse/Release	Single-strand breaks Abasic sites Base deamination 8-Oxoguanine lesions	Double-strand breaks Single-strand breaks Inter/intra-strand crosslinks
Repair pathways	Mismatch mediated repair (MMR)	Nucleotide excision repair (NER)	Direct damage reversal	Base excision repair (BER)	Non-homologous end-joining (NHEJ)	Homologous recombination (HR)