gene cloning

gene cloning (DNA cloning) The production of exact copies (clones) of a particular gene or DNA sequence using genetic engineering techniques. The DNA containing the target gene(s) is split into fragments using restriction enzymes. These fragments are then inserted into cloning vectors, such as bacterial plasmids or bacteriophages, which transfer the recombinant DNA to suitable host cells, such as the bacterium E. coli. Alternatively, complementary DNA is inserted into the vectors, or ‘naked’ DNA fragments can be taken up directly by a host bacterium from its medium (this is less efficient than vector transfer).

Inside the host cell the recombinant DNA undergoes replication; thus, a bacterial host will give rise to a colony of cells containing the cloned target gene. Various screening methods may be used to identify such colonies, enabling them to be selected and cultured. Gene cloning facilitates DNA sequencing; it also enables large quantities of a desired protein product to be produced (see expression vector): human insulin, for example, is now produced by bacteria containing the cloned insulin gene. See also positional cloning.