In semiconservative DNA replication, what best describes the composition of each daughter DNA double helix after one round of replication?

• A. Each daughter double helix is a mosaic of alternating old and new DNA segments within each strand.
• B. Each daughter double helix contains one parental (old) strand paired with one newly synthesized strand.
• C. Each daughter double helix contains two newly synthesized strands, and the parental DNA remains intact.
• D. Each daughter double helix contains two parental strands, and the newly synthesized strands form a separate double helix.

Answer: (B)

Verified step by step guidance

1. Understand the concept of semiconservative DNA replication: during this process, the double helix unwinds and each original (parental) strand serves as a template for the synthesis of a new complementary strand.
2. Recall that DNA strands are antiparallel and complementary, so the new strand is synthesized by matching bases to the parental strand (A pairs with T, and G pairs with C).
3. Recognize that after one round of replication, each daughter DNA molecule consists of one old (parental) strand and one newly synthesized strand, preserving half of the original molecule in each daughter helix.
4. Eliminate incorrect options by noting that the daughter helices are not mosaics of alternating old and new segments within a single strand, nor do they contain two new strands or two old strands paired together.
5. Conclude that the best description is that each daughter double helix contains one parental (old) strand paired with one newly synthesized strand, which is the hallmark of semiconservative replication.