The next type of DNA damage is Base mismatches.

DNA mismatch is a DNA defect occurring when two non-complementary bases are aligned in the same base-pair step of a duplex DNA. DNA mismatch can appear during replication of DNA, heteroduplex formation, mutagenic chemicals, ionizing radiation, or spontaneous deamination.

For this type of DNA damage, DNA mismatch repair (MMR) will take place.

MMR is a system for recognizing and repairing erroneous insertion, deletion, and misincorporation of bases that can arise during DNA replication and recombination, as well as repairing some forms of DNA damage.