The conclusion that G and C are present in DNA in equimolar amounts is credited to which scientist?

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

Answer: (A)

This is about Chargaff’s rules for DNA base composition. Erwin Chargaff showed that in any given DNA sample the amounts of guanine and cytosine are equal, and the amounts of adenine and thymine are equal as well. This G = C and A = T relationship means that guanine pairs with cytosine and adenine with thymine, which in turn implies a uniform pairing pattern across the two strands of the double helix. Chargaff’s observations were the key clue that guided the Watson–Crick model of DNA’s structure. While Watson and Crick proposed the double-helix arrangement and Rosalind Franklin provided crucial structural data, the specific conclusion that guanine and cytosine are present in equimolar amounts comes from Erwin Chargaff.