The recombinant DNA era gave birth to the era of molecular genetics and the biotechnology industry. Gene (or molecular) cloning refers to the isolation, transfer and propagation of a specific gene or DNA fragment using a cloning vehicle such as a bacterial plasmid. The circular plasmid containing the foreign DNA insert is grown in the host bacteria. The creation of DNA libraries using various vectors led to the identification of genes and the production of crucial biotechnology products such as insulin. Gene cloning was used to isolate and characterize genomic stretches of DNA as well as complementary DNA (cDNA), derived from the messenger RNA transcripts of genes.