Long before biotechnology discovered restriction enzymes, nature devised a way for pieces of DNA to move directly from one spot in an organism's genome to another, without any intermediate. These mobile elements, or transposons, were first described by Barbara McClintock in the 1940s during her studies of corn genetics. Transposons jump when an enzyme called transposase binds to specific sequences at the ends of the transposon DNA, cuts out the DNA and inserts the transposon at a new site on the same or different chromosome.

Transposons have been used in invertebrate, plant, and bacterial systems to randomly insert genes or markers into the genome, or for the directed incorporation of DNA into host organisms.