New ______________ position themselves along the parent strands through ______________ base pairing.

• A. Nucleotides; complementary
• B. Nucleotides; identical
• C. Nucleotides; random
• D. Nucleotides; noncomplementary

Answer: (A)

The main idea here is how DNA is copied with fidelity. During replication, new nucleotides align along each exposed parental strand by complementary base pairing. That means each base on the template strand binds its partner: A with T and C with G. So the new strand that is formed is complementary to its template and, together with the template, creates a correct, identical copy of the double helix information. If the added nucleotides were identical to the template, random, or noncomplementary, the hydrogen bonding wouldn't hold properly and the genetic information wouldn't be copied accurately. This complementary pairing is what makes DNA replication reliable and is central to the semi-conservative model, where each daughter molecule contains one old strand and one newly synthesized complementary strand.