A gene library is a collection of cloned DNA, usually from a specific organism. Just as a conventional library stores information in books and computer files, a gene library stores genetic information either for an entire genome, a single chromosome, or specific genes in a cell. For example, one can find the gene library of a specific disease such as cystic fibrosis, the chromosome where most cystic fibrosis mutations occur, or the entire genome of those individuals affected by the disease. To create a gene library, scientists extract the DNA of a specific organism and use restriction endonucleases to cut it. The scientists then insert the resulting fragments into vectors and make multiple copies of the fragments. The number of clones needed for a genomic library depends on the size of the genome and the size of the DNA fragments. Specific clones in the library are located using a DNA probe. (For more about DNA and genes, see the chapter “DNA, RNA, Chromosomes, and Genes.”)