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mismatch repair A form of DNA repair that replaces mismatched bases in newly replicated DNA in living cells. For example, if a guanine (G) on the template strand pairs with thymine (T) instead of the usual cytosine (C), the resulting abnormality in the DNA duplex is detected by the mismatch repair system. A length of strand containing the mismatched T is cut out and the gap is repaired with a new length containing the correct base (C), using the parental strand as template. The mismatch repair system closely follows the Y-shaped fork where the parental DNA unwinds and replication takes place, so enabling immediate correction of replication errors. It accounts for the vast majority of DNA repairs.