1957

Barbara McClintock discovered the breakage-fusion-bridge (bfb) cycle. Growing interested in the responses of the genome to tramatic events, McClintock joined forced with Lewis Stadler (who had shown the mutagenic effects of X rays on corn) and had sent McClintock the strains of the maize. McClinktock discovered and identified ring chromosomes. She then later realized that ring chromosomes were a special case of a special case of chromosomes broken by radiation. The broken ends sometimes fused to one another and formed a ring. This led McClintock to hypothesize the existence of a special structure at the chromosome tip, which she called the telomere, that would maintain chromosome stability. She described the breakage-fusion-bridge (bfb) cycle, a repeating pattern of chromosome behavior that was sometimes triggered by an initial breakage.

In the bfb cycle, broken chromosomes might fuse to the other member of the pair, forming a bridge that was then ripped apart at meiosis (or, in another form of the bfb cycle, at mitosis), thus beginning the cycle again.