(a)Oligonucleotide-directed mutagenesis ()Base-pair substitution Oligo binds to ssDNA Polymerization Replication in cell Oligo- SSDNA A (间Insertion (iii)Deletion (b)Cassette replacement (c)Deletion (d)Sets of deletions (e)PCR mutagenesis ·1 st PCR to obtain long primer Product■T ·2 nd PCR using long primer Product ■