What is site-directed mutagenesis and how is it performed?

Site-directed mutagenesis introduces specific mutations into DNA sequences. The most common method (QuikChange) uses complementary primers containing the desired mutation to amplify the entire plasmid in a PCR-like reaction. The methylated parental DNA is digested with DpnI (which only cuts methylated DNA), leaving only the mutant product for transformation. Other methods include overlap extension PCR and inverse PCR. Applications include studying protein function, creating enzyme variants, and investigating disease mutations. Modern approaches use Gibson assembly or CRISPR for more complex modifications.