Answer:
The discovery by James Watson and Francis Crick of the double helix, the twisted-ladder structure of deoxyribonucleic acid (DNA), in 1953 marked a landmark in the history of science and gave rise to modern molecular biology, which is largely concerned with understanding how genes regulate chemical processes
Rosalind Franklin's photo 51 had a diffraction pattern that suggested a double helix.
The two back bones had to run in opposite directions (the sugar phosphate backbones have to be on the outside with the bases inside) Levene had discovered that the number of A=T, and G=C
