3. DNA transposons

In the late 1940s and early 1950s, Barbara McClintock studied the mosaic color patterns of maize (corn) kernels and the unstable inheritance of this mosaicism. She found “controlling elements,” Ac (activator) and Ds (dissociator), that could be mobilized from one chromosomal position to another, leading to changes in kernel color when a suppressed gene containing a Ds element was reactivated and the Ds element moved to another genomic site. McClintock believed that these movable DNAs could regulate gene action and their mobility would in turn be regulated by environmental conditions, such as stress. In 1982, Nina Fedoroff, Sue Wessler, and M. Shure characterized the Ac and Ds elements, sequencing them and showing that Ac is ...

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