Gene cloning is a molecular biological technique that uses genetic engineering principles to create exact copies of clones of a specific gene or DNA sequence.

Recombinant DNA is created by fusing two or more DNA strands, combining DNA sequences that would not normally occur together. In other words, chosen DNA (or "interesting DNA") is inserted into an existing organismal genome, such as bacterial plasmid DNA or another type of vector.

The recombinant DNA can then be inserted into another cell, such as a bacterial cell, for amplification and, potentially, protein production. This is known as transformation, which is the genetic alteration of a cell caused by the uptake, incorporation, and expression of foreign genetic material. The discovery of restriction endonuclease enabled the development of recombinant DNA technology.

Restriction endonucleases, also known as restriction enzymes, are prokaryotic enzymes that recognise and cut DNA at specific sequences known as restriction sites. They are thought to have evolved as a defence mechanism against foreign DNA, such as viral DNA.

With the help of restriction enzymes, the DNA containing the target genes is fragmented. These fragments are then inserted into cloning vectors, such as bacteriophages or bacterial plasmids, which then transfer the recombinant DNA to appropriate host cells, such as the bacterium E.coli. The complementary DNA, on the other hand, is inserted into naked DNA fragments or vectors that can be taken up directly by the bacterium from its medium.