The genome is not static: genes move
      Phenomenon identified in 1940's by B. McClintock in maize: Nobel Prize 1983
                    [Keller: "A Feeling for the Organism"]

       Ac - Ds system in maize (Zea)
       Ds (Dissociator) locus causes chromosome breaks
            only when Ac (Activator) locus is present in trans configuration
                    Break affects expression of other genes in cis configuration
       Ds element may "jump" elsewhere in genome:
                    effect on expression of other genes is unstable,
                         depending on position of Ds

       Ac & Ds are transposable elements
            inverted terminal repeat - dsDNA reads the same in both orientations

           => elements may move from one position to another in genome

       Ac  has an ORF for a presumptive 'Transposase' gene
                     Ds is Ac with a defective Transposase gene

        Do transposable elements account for 'classical' mutants?
           'wrinkled' (rr) peas (Pisum)
                        defect of starch-branching enzyme (SBEI)
           'white eyes' in Drosophila
                        insertion of copia sequences
       Alu sequences in Homo
                  300 bp  element,  9 x 10⁵ copies => 10% of human genome is mobile