text: In the early days, chromosome walking from genetically linked DNA markers was used to identify and clone disease genes. However, the large molecular distance between known markers and the gene of interest was complicating the cloning process. In 1987, a human chromosome jumping library was constructed to clone the cystic fibrosis gene. Cystic fibrosis is an autosomal recessive disease affecting 1 in 2000 Caucasians. This was the first disease in which the usefulness of the jumping libraries was demonstrated. Met oncogene was a marker tightly linked to the cystic fibrosis gene on human chromosome 7, and the library was screened for a jumping clone starting at this marker. The cystic fibrosis gene was determined to localize 240kb downstream of the met gene. Chromosome jumping helped reduce the mapping "steps" and bypass the highly repetitive regions in the mammalian genome. Chromosome jumping also allowed the production of probes required for faster diagnosis of this and other diseases.