Protocol describes a method for generating isolated plaques from a stock of bacteriophage lambda. Each plaque derives from infection of a single bacterium by a single bacteriophage particle. Because each plaque contains the progeny of a single virus particle, the bacteriophages derived from a single plaque are essentially genetically identical to one another. - [Read Plating Bacteriophage Lambda Protocol]
Plaques formed by M13 bacteriophages or bacterial colonies transformed by plasmids carrying specific mutations can be detected by hybridization, using a radiolabeled oligonucleotide that forms a perfect duplex with the mutant sequence. Hybridization is carried out under conditions of low stringency that allow the radiolabeled oligonucleotide to anneal to both mutant and wild-type DNAs. - [Read Screening Recombinant Clones for Site-directed Mutagenesis by Hybridization to Radiolabeled Oligos]