eavage of a genome with restriction endonulease enzymes. Different "libraries"(3) of fragments may be obtained by using enzymes that recognize different sequences. The fragments are separated by electrophoresis, which permits their relative size to be approximate. (Figure 1)
             Stage 2. Recombinant DNA. Fragments of DNA are included in plasmid or virus "vehicles,"(4) which allow the fragments to be replicated as part of the plasmid or virus genome. It is essential to eliminate those plasmids or viruses which do not contain the fragment of DNA being moved.
             Stage 3. Cloning. The fragment- containing plasmids or viruses are introduced into bacterial cells. Each cell then reproduces, forming a clone of cells that all contain the fragment-bearing plasmid or virus. Each cell is maintained separately: together they consist of what is called a clone library.
             Stage 4. Screening. From the many clon
             ...