Who developed the double helix model of DNA?

• A. James Watson and Francis Crick
• B. Rosalind Franklin
• C. Gregor Mendel
• D. Charles Darwin

Answer: (A)

The main idea being tested is who first proposed the DNA double helix structure. James Watson and Francis Crick developed the first widely accepted model in 1953, showing DNA as two long strands wound into a right-handed helix with a sugar–phosphate backbone on the outside and nitrogenous bases paired inside. Their proposal integrated X-ray diffraction data (which helped reveal the helical shape) and Chargaff’s rules about base pairing (adenine pairs with thymine, guanine with cytosine), explaining how genetic information could be reliably copied. The model also suggested a mechanism for replication: the two strands could separate and serve as templates for new complementary strands. Rosalind Franklin contributed crucial data through her X-ray crystallography work that informed the model, although she did not publish the final structure herself. Gregor Mendel is known for genetics before the DNA era, and Charles Darwin for evolution; neither developed the DNA double-helix model.