What does semi-conservative replication mean?

• A. Each daughter DNA molecule contains two parental strands.
• B. Each daughter DNA molecule consists of one parental strand and one newly synthesized strand.
• C. Each daughter DNA molecule contains two newly synthesized strands.
• D. Each daughter DNA molecule contains one parental strand and one strand of RNA primer.

Answer: (B)

In semi-conservative replication, each daughter DNA molecule ends up with one strand from the original double helix (the parental strand) and one newly synthesized strand. The two parental strands unwind and serve as templates for making complementary new strands, so after replication there are two DNA molecules, each consisting of one old and one new strand. RNA primers are only temporary starting points for synthesis; they’re later removed and replaced with DNA, so the final DNA molecule contains DNA on both strands, not RNA. That’s why the correct description is one old strand plus one new strand, not two old or two new strands.