McClintock was widely credited with discovering transposition after other researchers finally discovered the process in bacteria, yeast, and bacteriophages in the late 1960s and early 1970s. During this period, molecular biology had developed significant new technology, and scientists were able to show the molecular basis for transposition. In the 1970s, Ac and Ds were cloned by other scientists and were shown to be class II transposons. Ac is a complete transposon that can produce a functional transposase, which is required for the element to move within the genome. Ds has a mutation in its transposase gene, which means that it cannot move without another source of transposase. Thus, as McClintock observed, Ds cannot move in the absence of Ac. Spm has also been characterized as a transposon. Subsequent research has shown that transposons typically do not move unless the cell is placed under stress, such as by irradiation or the breakage-fusion-bridge cycle, and thus their activation during stress can serve as a source of genetic variation for evolution. McClintock understood the role of transposons in evolution and genome change well before other researchers grasped the concept. Nowadays, Ac/Ds is used as a tool in plant biology to generate mutant plants used for the characterization of gene function.
McClintock was widely credited with discovering transposition after other researchers finally discovered the process in bacteria, yeast, and bacteriophages in the late 1960s and early 1970s. During this period, molecular biology had developed significant new technology, and scientists were able to show the molecular basis for transposition. In the 1970s, Ac and Ds were cloned by other scientists and were shown to be class II transposons. Ac is a complete transposon that can produce a functional transposase, which is required for the element to move within the genome. Ds has a mutation in its transposase gene, which means that it cannot move without another source of transposase. Thus, as McClintock observed, Ds cannot move in the absence of Ac. Spm has also been characterized as a transposon. Subsequent research has shown that transposons typically do not move unless the cell is placed under stress, such as by irradiation or the breakage-fusion-bridge cycle, and thus their activation during stress can serve as a source of genetic variation for evolution. McClintock understood the role of transposons in evolution and genome change well before other researchers grasped the concep:t. Nowadays, Ac/Ds is used as a tool in plant biology to generate muta.nt plants used for the characterization of gene function.