Technology & Medicine › Atomic & space age › DNA double helix
Rosalind Franklin and Photo 51
1920–1958; Photo 51 May 1952· Person· Germs, drugs & genetics
Well documentedSolid records, physical evidence or scientific consensus.
Rosalind Franklin was an English chemist whose X-ray images of DNA, especially Photo 51, revealed its helical shape.
See it on the Technology & Medicine map →How it works
At King's College London in 1951–53, Franklin used X-ray crystallography: shining X-rays through fibers of DNA and reading the pattern of scattered spots. In May 1952 she and her student Raymond Gosling recorded Photo 51, a sharp X-shaped pattern that signals a helix. Her measurements also showed that DNA's sugar-phosphate backbone lies on the outside. She then studied virus structure at Birkbeck College until her death from ovarian cancer in 1958, aged 37.
Why it mattered
Her data were essential to the double-helix model, and her story has become the best-known example of women scientists' work being overlooked.
Legacy and how we know
Her lab notebooks, Photo 51 itself, her April 1953 Nature paper printed alongside Watson and Crick's, and biographies by Anne Sayre (1975) and Brenda Maddox (2002).
Still unknown or debated
How close she was to solving the structure herself is debated; her drafts show her moving toward a two-chain helix in early 1953.
Connections (2)
▸X-rays (Röntgen) were used in crystallography by Rosalind Franklin and Photo 51Well documented
The connection
Röntgen's X-rays have wavelengths about as small as the spacing between atoms. In 1912–13 Max von Laue and the Braggs showed that crystals scatter X-rays into patterns revealing how their atoms are arranged. Franklin, an expert in this X-ray crystallography, applied it to DNA fibers to reveal their shape.
When and how
Würzburg, 1895 (Röntgen); Munich, Leeds and Cambridge, 1912–13 (von Laue; William and Lawrence Bragg); King's College London, 1951–53 (Franklin).
How we know
Franklin's notebooks and papers detail her X-ray methods; Lawrence Bragg, a founder of the technique, headed the Cambridge lab where Watson and Crick worked.
Debates and open questions
Did Franklin's insistence on data before models slow her, or protect her from errors like Watson and Crick's failed 1951 model? Opinions differ.
▸Rosalind Franklin and Photo 51 supplied the key X-ray image for the DNA double helixWell documented
The connection
Photo 51's X-shaped pattern told Watson at once that DNA is a helix, and its spacing gave key dimensions. Franklin's data, summarized in a 1952 lab report, also placed the backbone outside and fixed its repeat distances. Watson and Crick used both, without her permission, to build their model in early 1953.
When and how
King's College London, May 1952 (Photo 51, taken with Raymond Gosling); Maurice Wilkins showed it to Watson in January 1953; Cambridge model built in March 1953.
How we know
Watson's own memoir, The Double Helix (1968), describes seeing the photo, and Franklin's paper ran in the same Nature issue as the model.
Debates and open questions
Historians debate whether her data were 'stolen' or shared through normal if careless channels; a 2023 Nature essay argued she was an equal contributor.