Current researchers have developed gene transfer systems on the basis of conservative transposition which can integrate new DNA in both invertebrates and vertebrate genomes. Scientists alter the genetic sequence of a transposon in a laboratory setting, then insert this sequence into a vector which is then inserted into a target cell. The transposase coding region of these transposons is replaced by a gene of interest intended to be integrated into the genome. Conservative transposition is induced by the expression of transposase from another source within the cell, since the transposon no longer contains the transposase coding region to be self sufficient. Generally a second vector is prepared and inserted into the cell for expression of transposase. This technique is used in transgenesis and insertional mutagenesis research fields. The Sleeping Beauty transposon system is an example of gene transfer system developed for use in vertebrates. Further development in integration site preferences of transposable elements is expected to advance the technologies of human gene therapy.