Transposons are sequences of DNA that can move around in a genome. In a laboratory setting, transposons can be used to both introduce genes into an organism’s genome (see figure) and to disrupt endogenous genes at the site of insertion. In both of these cases, transposons combine the advantages of viruses and naked DNA while eliminating some of the drawbacks. Specifically, viruses are able to infect and replicate in host cells, but they are susceptible to cells’ defense mechanisms. The use of non-viral vectors, like transposons, avoids many, though not all, of these defenses. For some applications of genome engineering - such as certain forms of gene therapy - avoiding the use of viruses is also important for social and regulatory reasons.