In May 1952, British chemist Rosalind Franklin captured one of the most significant photos in scientific history: an X-ray diffraction photograph of DNA. The process involved exposing DNA to X-rays for 62 hours at King’s College London. Franklin labeled the image “Photo 51,” as it was the 51st in a series of photos she had taken. The photo and her unpublished research on it suggested that DNA had a helical structure—an insight that ultimately allowed scientists to understand DNA’s function.

Franklin came to King’s College London in 1951 to join biophysicists John Randall and Maurice Wilkins in their work studying molecular structure with X-ray diffraction. At the time, scientists did not understand the structure or genetic function of DNA. Wilkins and Franklin divided the work of studying DNA between themselves, and PhD student Raymond Gosling assisted Franklin in the lengthy process of taking Photo 51.

Franklin recognized that Photo 51 suggested DNA had a helical structure, and she mentioned this in her notes. Gosling showed Wilkins the photo, and in early 1953, Wilkins shared the photo and Franklin’s data with American biologist James Watson. Watson later claimed this was a significant moment that led him and British biophysicist Francis Crick to conclude that DNA had a double-helix structure.

Recent biographers of Franklin and Crick have argued that, at the time, the scientists involved in this research may have viewed the discovery of DNA’s structure as collaborative, rather than the singular achievement of Watson and Crick. In the same April 1953 issue of Nature in which Watson and Crick published a paper about the structure of DNA, Franklin and Gosling published their own paper about evidence for a “2-Chain Helix,” and Wilkins published another paper about DNA structure with two other authors.

In 1962, Wilkins, Watson and Crick jointly received a Nobel prize for the discovery of DNA’s molecular structure. Franklin, who had died in 1958 from ovarian cancer, was ineligible for the award because the Nobel Foundation does not award prizes posthumously. However, Watson’s 1968 book, The Double Helix: A Personal Account of the Discovery of the Structure of DNA, centered himself and Crick in the story of the discovery and painted a jarringly unflattering portrait of Franklin.

Watson’s book helped provoke debate about, and spark interest in Franklin’s role in the discovery of DNA’s structure. Since its publication, historians and scientists have worked to clarify and confirm Franklin’s important role in the scientific discovery.