DNA molecular model, 1993.
© Science Museum / Science & Society Picture Library
A replica of the original DNA model built by Francis Crick (b 1916) and James Dewey Watson (b 1928) while working in the Medical Research Council Unit at the Cavendish Laboratory in Cambridge in 1953. They discovered that DNA (deoxyribonucleic acid) is made up of a double helix (ie two strands) of phosphate 'backbones' joined by complementary sequences of base pairs (units of genetic information). To replicate, the two chains unwind and act as templates.