Crick and Watson�s DNA molecular model, 1953.

UNITED KINGDOM - FEBRUARY 05: This reconstruction of the double helix model of DNA (deoxyribonucleic acid) contains some of the original metal plates used by Francis Crick (b 1916) and James Dewey Watson (b 1928) to determine the molecular structure of DNA. It is constructed out of metal plates and rods, arranged helically around a retort stand, and shows one complete turn of the famous double helix. The metal plates represent the four bases, whose complementary arrangement immediately suggested a possible copying mechanism for the genetic material. Crick and Watson made their discovery while working in the medical Research Council Unit at the Cavendish Laboratory in Cambridge. (Photo by SSPL/Getty Images)