The contribution of physics in the discovery of the double helix

Schrodinger's prediction of genes and Delbruck's determination of genetic matter are reviewed. X-ray diffraction , including Bragg's equation in crystallography, the Fourier transform of helical structures, and Wilkins' experimental determination of the double helix are discussed. The molecular model method is presented, with details of the bond angles and lengths, the theory of hybrid bond orbitals, formulae for the tetrahedral orbitals, and effects of the hydrogen bond.