Photo 51

Photo 51 is an X-ray diffraction image of DNA fibers, made by Raymond Gosling under Rosalind Franklin’s supervision in 1952. Its distinctive cross-shaped pattern provided evidence that DNA has a helical structure.

X-ray crystallography: A method for determining atomic and molecular structures from X-rays scattered by ordered matter. Photo 51 is a fiber-diffraction image, a crystallographic method for inferring molecular structure.
Raymond Gosling: A British scientist who made key X-ray diffraction images of DNA while working with Rosalind Franklin. Gosling recorded Photo 51 under Franklin’s supervision.
Double-helix model of DNA: A structural model in which two DNA strands wind around a shared axis, with paired bases inside. Photo 51 supported the helical geometry central to the model.
A-form DNA: A dehydrated, right-handed DNA conformation with a diffraction pattern distinct from B-form DNA. Franklin distinguished the A-form pattern from the B-form pattern shown in Photo 51.
X-ray diffraction: The scattering of X-rays by matter, producing patterns that reveal information about its structure. The image records X-rays scattered by aligned DNA fibers.
Rosalind Franklin: A British chemist whose X-ray diffraction work contributed to determining DNA’s structure. Franklin supervised the experiment and analyzed the DNA diffraction data.
Watson and Crick 1953 paper: The Nature paper that proposed a double-helical structure for DNA in 1953. The paper’s model drew on evidence from DNA diffraction, including Photo 51.
DNA fiber diffraction photograph 51: A specific B-form DNA diffraction photograph made by Raymond Gosling in 1952. Photo 51 is often contrasted with Franklin and Gosling’s less iconic A-form diffraction images.
Bragg's law: A relation connecting X-ray wavelength, crystal-plane spacing, and diffraction angle. Diffraction angles in the image encode repeating distances within DNA.
Maurice Wilkins: A British physicist who studied DNA by X-ray diffraction at King’s College London. Wilkins showed the image to James Watson without Franklin’s prior knowledge.

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