Whose X-ray diffraction work provided crucial evidence that helped Watson and Crick deduce the DNA double helix?

Introduction / Context:The double-helix model of DNA proposed by James Watson and Francis Crick in 1953 relied on converging lines of evidence: base-pairing rules, fiber diffraction, and chemical constraints. Understanding whose data underpinned the helix geometry is part of the history of science.

Given Data / Assumptions:

• X-ray diffraction patterns of DNA fibers constrain helical pitch and symmetry.
• Contemporaneous biochemical data (e.g., Chargaff’s ratios) limited base pairing possibilities.
• Multiple scientists contributed to the era’s insights.

Concept / Approach:Rosalind Franklin’s high-resolution X-ray diffraction photographs (notably Photo 51, taken by her student Raymond Gosling) revealed helical features, spacing of stacked bases (~3.4 Å), and dimensions consistent with a two-strand helix, guiding model building.

Step-by-Step Solution:

Verification / Alternative check:Historical accounts and primary sources credit Franklin’s patterns with helical inference and correct helical parameters used by Watson and Crick.

Why Other Options Are Wrong:

• W. H. Bragg: Nobel laureate in X-ray crystallography methods, but not the DNA fiber data.
• Linus Pauling: proposed a triple-helix model that was incorrect for DNA.
• Joshua Lederberg: genetics pioneer; not responsible for DNA X-ray fiber images.
• Erwin Chargaff: provided base ratio rules; crucial but not X-ray diffraction.

Common Pitfalls:Attributing “X-ray evidence” generically to famous names without distinguishing the specific DNA fiber data.

Final Answer:Rosalind Franklin