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DNA double helix (Watson & Crick, 1953)
1953 (Watson & Crick, using Rosalind Franklin's data)· Event· Microbes & cells
Well establishedStrong fossil, genetic or geological evidence.
In 1953 James Watson and Francis Crick worked out that DNA is two strands twisted around each other, paired base by base.
See it on the Life map →What happened
Working at Cambridge, Watson and Crick built metal and cardboard models guided by Rosalind Franklin's X-ray data and Erwin Chargaff's finding that DNA's bases come in matching amounts. Their structure: two sugar-phosphate backbones winding on the outside, with bases inside pairing A with T and G with C. Published in Nature on 25 April 1953, the paper noted dryly that the pairing 'immediately suggests a possible copying mechanism'. Watson, Crick and Maurice Wilkins shared the 1962 Nobel Prize.
Why it matters
It showed how genetic information is stored and copied, launching molecular biology, DNA sequencing, biotechnology and, eventually, gene editing.
Think of it like
Like a zipper: pull the two sides apart and each half guides the building of a new, matching partner.
The evidence (fossils, genes, rocks)
The one-page Nature paper, printed alongside papers by Wilkins's and Franklin's groups; confirmed in 1958 when Matthew Meselson and Franklin Stahl showed DNA copies itself as the model predicted.
Still debated
How credit should be shared, especially with Franklin, is still argued over; the structure itself is settled.
Inside this (1)
Connections (2)
▸Rosalind Franklin provided key X-ray evidence for DNA double helix (Watson & Crick, 1953)Well established
The connection
Franklin's X-ray images, especially Photo 51, showed DNA was a helix and gave key measurements, and her analysis put the sugar-phosphate backbone on the outside. Watson saw the photo in January 1953, and Crick saw her data in a research report. These guided their final model, published in April 1953.
When and how
King's College London, 1951–1953, with student Raymond Gosling; her data reached Watson and Crick in Cambridge via Maurice Wilkins and Max Perutz.
The evidence
Watson's 1968 memoir describes seeing Photo 51; their paper acknowledged Franklin's 'unpublished experimental results', and her own data appeared in the same Nature issue.
Debates and open questions
Whether her data were used fairly, since she was never asked; Aaron Klug's 1968 study of her notebooks argued she was nearing the structure herself, though how close is debated.
▸DNA double helix (Watson & Crick, 1953) led to the cracking of The universal genetic codeWell established
The connection
The 1953 double helix showed that DNA stores information as a sequence of four chemical letters. That raised the question of how a letter sequence specifies a protein. Researchers then showed the cell reads three-letter words, each naming an amino acid, and matched all 64 words by 1966.
When and how
Watson and Crick at Cambridge, 1953; Crick and Sydney Brenner showed triplet reading in 1961; Nirenberg and Matthaei decoded the first word, UUU, in 1961.
The evidence
Published experiments and the 1968 Nobel Prize to Nirenberg, Khorana and Holley; the code has since been confirmed in thousands of sequenced genomes.
Debates and open questions
Little debate about the link itself; historians discuss the credit due to Rosalind Franklin and to the many teams that raced to decode it.