Molecular Cloning

"The main idea of molecular cloning is to insert a DNA segment of interest into an autonomously replicating DNA molecule, a so-called cloning vector or vehicle, so that the DNA segment is replicated with the vector.
Cloning such a chimeric vector in a suitable host organism such as E.coli or yeast results in the production of large amounts of the inserted DNA segment.
If a cloned gene is flanked by the properly positioned control sequences for transcription and translation, the host may also produce large quantities of the RNA and protein specified by that gene." - Voet D. & Voet J.G., (2004) Chapter 5, Biochemistry 3rd edition, Wiley.