DNA that has been given a piece of foreign DNA. A recombinant DNA molecule is thus composed of DNA from at least two different sources.
Recombinant bacteria caused by the bacteria naturally through conjugation exchange of DNA material. In higher organisms, recombination occurs naturally when DNA is exchanged between two homologous chromosomes (chromosomes in the same pair) during gamete formation.
In both these cases, recombination occurs within the same species; it is homologous. The result from homologous recombination is that in nature are other combinations of genes than those that originally existed, and the process contributes greatly to the enormous genetic variation seen in humans and other species. Using genetic engineering can be targeted splicing together DNA molecules from multiple sources and create new recombinant DNA molecules.