Recombinant DNA technology, as its name implies, relies on techniques that combine DNA from one source with DNA from another. Typically the DNA of interest (passenger DNA) is combined with another DNA molecule (vector DNA) that serves to ensure its replication and selection . Major obstacles to be overcome for any DNA cloning include purification and isolation of the DNA to be cloned, as well as the identification and selection of the cloned DNA of interest.
Today, cloning a gene is often the first step in analysis of the gene. Cloned genes can be easily studied, manipulated, sequenced and amplified. Often a gene product has important commercial or medical value, or both. One of the early eukaryotic genes cloned in E. coli was the gene for somatostatin, a hormone used to treat dwarfism. The amount of hormone previously purified from millions of sheep brains could now be produced in a few liters of bacterial culture broth. With examples such as this, the power of cloning is obvious.