Evidence for 2-chain helix in crystalline structure of sodium deoxyribonucleate.

Franklin and Gosling's completed Patterson synthesis of the A-form of DNA, based on work begun in 1952, represents the first independent confirmation that the Watson-Crick double-helix model was correct. "We suggest that the unit in structure A is, as in Structure B, two co-axial helical chains running in opposite directions" (p. [5]). "The demonstration of the correctness of the structure is thus doubly convincing because the double-helical structure may be arranged to fit the X-ray data of both forms." (Klug, "Rosalind Franklin and the Discovery of the Structure of DNA" Nature 219 [1968]: 808). Judson, Eighth Day of Creation, p. 161.