DNA replication is described as semiconservative. Which statement best explains why DNA is called semiconservative?

• A. Each daughter DNA molecule contains two newly synthesized strands with no parental DNA retained.
• B. Each daughter DNA molecule contains one parental (old) strand and one newly synthesized strand.
• C. Parental DNA is completely conserved as an intact double helix while a completely new double helix is synthesized separately.
• D. Each daughter DNA molecule contains a mixture of old and new DNA segments interspersed within each strand.

Answer: (B)

Verified step by step guidance

1. Understand the concept of DNA replication: DNA replication is the process by which a DNA molecule makes a copy of itself. This is essential for cell division.
2. Recall the meaning of 'semiconservative' replication: In semiconservative replication, each of the two resulting DNA molecules contains one original (parental) strand and one newly synthesized strand.
3. Compare the options given: Identify which statement correctly describes that each daughter DNA molecule retains one old strand and one new strand, rather than having all new strands or mixed segments.
4. Eliminate incorrect options: For example, the option stating both strands are newly synthesized is incorrect because it ignores the parental strand retention; similarly, the option about parental DNA being completely conserved as an intact double helix is incorrect because the original strands separate during replication.
5. Conclude that the correct explanation is that each daughter DNA molecule contains one parental (old) strand and one newly synthesized strand, which aligns with the semiconservative model of DNA replication.