In semi-conservative replication, what is the composition of each daughter DNA molecule?

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

Answer: (A)

In semi-conservative replication, each new DNA molecule contains one strand that came from the original double helix and one newly synthesized strand. The two parent strands separate, and each serves as a template for a complementary new strand, produced by DNA polymerase in the 5' to 3' direction. After replication, both daughter molecules are made of two DNA strands, with one old strand and one new strand, so genetic information is preserved in each generation. RNA primers are only temporary starting points for synthesis and are removed and replaced with DNA, so the finished molecules contain two DNA strands rather than an RNA segment. This is why the correct description is one parental strand and one newly synthesized strand per daughter DNA molecule.