In semiconservative DNA replication, the copying of genetic information is efficient because:

• A. Replication proceeds by randomly assembling nucleotides without needing an existing strand, which speeds synthesis.
• B. Each original (parental) strand serves as a template for synthesis of a complementary new strand via base-pairing rules.
• C. Both parental strands remain together and a completely new double helix is synthesized separately, doubling the DNA without templates.
• D. Only one parental strand is copied while the other is degraded, reducing the amount of DNA that must be synthesized.

Answer: (B)

Verified step by step guidance

1. Understand the concept of semiconservative DNA replication: each of the two parental DNA strands serves as a template for the synthesis of a new complementary strand.
2. Recall that DNA replication relies on base-pairing rules, where adenine pairs with thymine and cytosine pairs with guanine, ensuring accurate copying of genetic information.
3. Recognize that during replication, the double helix unwinds and each original strand guides the formation of a new strand, resulting in two DNA molecules each composed of one old and one new strand.
4. Contrast this with other hypothetical models, such as conservative replication (where parental strands stay together) or dispersive replication (random assembly), to understand why semiconservative replication is efficient and accurate.
5. Conclude that the efficiency comes from using the original strands as templates, which ensures fidelity and speed in copying genetic information.