Tandem genetic duplications in phage lambda. IV. The locations of spontaneously arising tandem duplications.

Twenty-four spontaneously arising, long DNA addition derivatives of phage lambda have been isolated by two methods (one physical, one genetic) based on phage DNA content. All are shown to contain a tandem duplication of phage DNA by a number of criteria. The location of the duplicated segment in each has been determined by electron microscopy of DNA hereroduplexes. The duplications are found to lie at random throughout the chromosome, with no preferential locations for endpoints. This rules out the possibility that duplications are formed by crossing-over at regions of homology on the phage chromosome.