What best describes the semi-conservative nature of DNA replication?

• A. Each new molecule contains two original strands.
• B. Each new molecule contains one original and one new strand.
• C. Replication results in two original molecules.
• D. Both strands are degraded and re-synthesized.

Answer: (B)

DNA replication is semi-conservative: every new double helix contains one strand that was already present in the parent and one newly synthesized strand. As the two parental strands separate, each serves as a template for a complementary new strand, so the resulting daughter molecules are hybrids with one old strand and one new strand. This arrangement preserves half of the original genetic material in each daughter cell, which is supported by classic experiments and explains why the correct description is one original plus one new strand in each molecule. The other descriptions would imply both strands are old in a daughter, both are new, or that strands are torn down and rebuilt entirely, none of which reflects how replication truly preserves parental information.