Which team is credited with proposing the double-helix model after weighing evidence?

• A. Rosalind Franklin
• B. Maurice Wilkins
• C. James Watson and Francis Crick
• D. Erwin Chargaff

Answer: (C)

Understanding how evidence from different experiments comes together to reveal a molecular shape is what's being tested. James Watson and Francis Crick are the ones credited with proposing the double-helix structure after weighing the available evidence. They integrated Rosalind Franklin and Maurice Wilkins’ X-ray diffraction data, which hinted at a helical form with a regular width, with Chargaff’s observation that base pairing is specific (A pairs with T, G pairs with C). By combining these clues in a physical model, they showed a pair of anti-parallel strands winding into a right-handed helix, with the sugar-phosphate backbone on the outside and complementary bases inside, held together by specific base pairs. This synthesis of diverse lines of evidence led to the proposed structure, rather than any single data point or rule alone. Franklin and Wilkins provided crucial data, and Chargaff’s rules guided the pairing, but Watson and Crick are the duo who formulated the actual double-helix model.