The Ac/Ds transposable element system of maize was first discovered by Barbara McClintock, leading to her 1983 Nobel Prize in Medicine. The Ac Activator element is autonomous, whereas the Ds Dissociation element requires an Activator element to transpose. Ac was initially discovered as enabling a Ds element to break chromosomes. Both Ac and Ds can also insert into genes, causing mutants that may revert to normal on excision of the element. These elements were first isolated and sequenced By Federoff et al. 1983 using insertions of Ac and Ds into the well-studied Waxy(Wx1) gene.