Figure 4.

'A' form DNA. An example of an X-ray diffraction pattern obtained by Rosalind Franklin and Raymond Gosling from 'A' form DNA, which is distinct from the 'B' structure predominately found in vivo. Before embarking on the determination of the 'B' form structure, Franklin and Gosling had set out to determine the structure of 'A' form DNA from first principles. © Raymond Gosling; reproduced with permission.