McClintock's challenge in the 21st century.

In 1950, Barbara McClintock published a Classic PNAS article, "The origin and behavior of mutable loci in maize," which summarized the evidence leading to her discovery of transposition. The article described a number of genome alterations revealed through her studies of the Dissociation locus, the first mobile genetic element she identified. McClintock described the suite of nuclear events, including transposon activation and various chromosome aberrations and rearrangements, that unfolded in the wake of genetic crosses that brought together two broken chromosomes 9. McClintock left future generations with the challenge of understanding how genomes respond to genetic and environmental stresses by mounting adaptive responses that frequently include genome restructuring.