Diagram of chromosome breakage. Diagram showing the breakage-fusion-bridge (BFB) cycle for chromosomes that occurs during cell division. These diagrams, dated 30 August 1950, are from the papers of US cell geneticist Barbara McClintock (1902-1992). McClintock was awarded the 1983 Nobel Prize in Physiology or Medicine for her work on mobile genetic elements (transposable elements) in the 1940s and 1950s. The work on the BFB cycle, shown here, was carried out in the late 1930s. The BFB cycle, a form of chromosomal instability, is where chromatids can break and fuse during cell division. This mechanism is thought to play a role in cancer formation.