If a completely radioactive double stranded DNA molecule undergoes two rounds of replication in a solution free of radioactive label. What is the radioactivity status of the resulting four double stranded DNA molecules: (A) 50% of the DNA molecules have no radioactivity, (B) 2 DNA molecules have radioactivity in both strands, (C) I DNA molecule has radioactivity in both strands, (D) All 4 DNA molecules have radioactivity
Answer is A. DNA replication is semi conservative. Thus 2 DNA molecules have one strand with radioactivity and other 2 DNA molecules have no radioactivity.