When they transpose along, or between, chromosomes, they cause inactivation of neighbouring genes. In some cases, they also result in structural instability at the sites of integration, causing chromosomes to break easily at these sites. When control elements leave a certain region, the previously inactived genes resume normal functions. Control elements can be classified into groups. By doing so, the superior element controls the exact time during development when transpositions are to occur.
Control elements can assume different states.
They can be part of regulatory systems consisting of two or more elements. They can also appear as independent or autonomous elements. Some elements act by programming neighbouring genes to become active at a later time, which may be several cell generations later. McClintock's experiments were carried out with great ingenuity and intellectual stringency. They reveal a whole world of previously unknown genetic phenomena.