The general approach to clone DNA is as follow:
DNA is extracted from cells and cut by the restriction endonuclease enzyme into several segments. Plasmid DNA is also cut by the same enzyme and then the plasmid and cell DNA are mixed together and joined with an enzyme DNA ligase to give recombined DNA. Each of the resulting plasmids contain a piece of DNA from the cell. Under appropriate conditions bacteria absorb the recombination plasmids. If the host bucterium is sensitive to the antibiotics tetracycline and ampicilin, it will not grow in their presence. However, the plasmids with its resistance genes all the bacterium to grow. When a single bacteria divides on an agar plate, each of the millions of daughter cell carries an identical copy of the original plasmid containing the inserted DNA from the cell. By this technique the total nuclear DNA from a cell may be divided into many clones, each clone having a point of DNA of the cell from which it was extracted. Such a collection of thousands of clones constitute a genomic library.[37 ]