text: This technique is an extension of "chromosome walking" that allows larger "steps" along the chromosome.
  If steps of length N kb are desired, very high molecular weight DNA is necessary. Once isolated, it is partially digested with a frequent-cutting restriction enzyme (such as MboI or BamHI). Next, obtained fragments are selected for size which should be around N kb in length. DNA must then be ligated at low concentration to favour ligation into circles rather than formation of multimers. A DNA marker (such as the amber suppressor tRNA gene supF) can be included at this time point within the covalently linked circle to allow for selection of junction fragments. Circles are subsequently fully digested with a second restriction enzyme (such as EcoRI) to generate a large number of fragments. Such fragments are ligated into vectors (such as a λ vector) which should be selected for using the DNA marker introduced earlier. The remaining fragments thus represent the library of junction fragments, or "jumping library".
  The next step is to screen this library with a probe that represents a "starting point" of the desired "chromosome hop", i.e. determining the location of the genome that is being interrogated. Clones obtained from this final selection step will consist of DNA that is homologous to our probe, separated by our DNA marker from another DNA sequence that was originally located N kb away (thus being called "jumping").
  By generating several libraries of different N values, eventually the entire genome can be mapped, allowing movement from one location to another, while controlling direction, by any value of N desired.