Answer: Adenine pairs with Thymine, Cytosine pairs with Guanine. The base pairing rules states that wherever adenine occurs in one strand of DNA, thymine will be found in the complementary strand and wherever guanine occurs in one strand, cytosine will be found in the complementary strand.
Explanation: In a double stranded helical DNA molecule, the bases pair with each other to form the middle steps while the phosphate group and the deoxyribose form the phosphodeoxyribose backbone. DNA base pairing follows the Watson and Crick base pairing rules which states that adenine pairs with thymine while cytosine pairs with guanine. In the DNA base pairing, adenine forms a double bond with thymine while cytosine forms a triple bond with guanine.
