these molecules can join with each other by the base-pairing between their sticky ends. The union can be made permanent by another enzyme, DNA ligase, which forms covalent bonds between the molecules. The result is a molecule of recombinant DNA (rDNA). The ability to produce recombinant DNA molecules has not only revolutionized the study of genetics but has laid the foundation for much of the biotechnology industry. In humans, recombinant DNA is the basis of gene therapy, in which the DNA is introduced
             ...