Practice question

Tandem repeats create duplicated restriction recognition sites at regular intervals, altering expected fragment number and size predictably. Simple single enzyme digestion that should linearize plasmid may instead produce multiple bands or an unusually large fragment if repeats are head-to-tail and sites are duplicated. Restriction mapping using several enzymes, double digests, and comparison of observed versus predicted fragment patterns reveals duplications, insertions, or rearrangements. While PCR and sequencing can ultimately confirm repeat structure, initial screening by restriction mapping provides quick physical evidence of repeat expansion, orientation, and stability needed for plasmid quality assessment.