Question

How did Watson and Crick determine base pairing?

Answer 1

Their model of the DNA molecule showed that the hydrogen bonds could create a nearly perfect fit between nitrogenous bases along the center of the molecule. But the bonds could only form between adenine and thymine, and between cytosine and guanine.

Answer 2

They were the first ones to build a model that showed the hydrogen bonds that could make a almost perfect fit between nitrogenous bases along the center of the molecule. This could only happen if the bonds could form between adenine and thymine, and between cytosine and guanine.