This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: "Photo 51" was a cleaner version of an earlier X-ray image, "Photo 49," that Rosalind Franklin had already used to calculate key features of DNA, challenging long-held assumptions about her role in the discovery of the double helix. The new research from King's College London and the Science History Institute, published in the Journal of the History of Biology, challenges the long-held belief that Franklin did not recognize the significance of "Photo 51." The research shows that "Photo 51" was a carefully planned, high-quality repeat of an earlier image, "Photo 49," that Franklin had already used to calculate key features of DNA's helical structure.
"Photo 49" contained a blemish caused by a component inside the X-ray camera slipping across the film and obscuring part of the image. Despite this, Franklin was able to extract useful information from the photograph and use it to determine key features of the structure of the DNA molecule. At this point, Franklin had not established exactly how many strands made up the DNA molecule—whether it was a single, double or triple helix.
But the research shows that she already knew that the X-ray pattern could provide important information about DNA's helical structure. Franklin and her graduate student Raymond Gosling took "Photo 51" at King's College London in 1952. The image was produced by firing X-rays at DNA and recording the pattern created when the X-rays scattered from the DNA molecules.
The resulting X-shaped pattern provided evidence that DNA had a helical structure. The image became famous after it was shown in early 1953, without Franklin's knowledge, to James Watson, who was working with Francis Crick at the University of Cambridge. Less than two months later, Watson and Crick had built their double-helical model of DNA; it was published in Nature, alongside a paper by Franklin and Gosling describing "Photo 51." Watson later wrote that seeing the photograph had helped him and Crick develop their model of DNA.
However, subsequent accounts have often portrayed Franklin as having failed to recognize the significance of the image herself. The new research challenges this version of events. The researchers reached their conclusions by examining laboratory notebooks, manuscripts, photographs and other historical records held in collections in Philadelphia, Cambridge and London.
They also examined Franklin's original X-ray camera and photographic slides held in the archives of King's College London. Study co-author Alistair Sponsel began reexamining Franklin's DNA research in 2025 after the Science History Institute acquired the History of Molecular Biology Collection from the J. The collection includes Franklin's own copy of "Photo 51," alongside notebooks, correspondence, photographs and other material documenting the history of molecular biology.
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