To follow up on your previous experiment with DNA replication in virus U238, conduct another Meselson-Stahl type experiment, again allowing a virus to replicate in the presence of "heavy" nitrogen until both strands of its genome are "heavy." In this experiment, you allow virus U238 to undergo two complete rounds of replication in the presence of "light" nitrogen. What ratio of "heavy" to "light" viral DNA would you expect to find at the end of two complete rounds of replication?
A)1:3
B)2:2
C)3:1
D)None of the other answer options is correct.

Question

Quizplus · Accepted Answer

After two rounds of replication in the presence of light nitrogen, the original heavy DNA would have been diluted across the generations. In the first round of replication, each new DNA molecule consists of one heavy strand and one light strand, resulting in a 1:1 ratio of heavy to light DNA. In the second round of replication, the heavy-light DNA molecules replicate, producing molecules with two light strands and further diluting the heavy DNA. Thus, after two rounds, there would be one molecule with heavy DNA (from the first replication round) and three with light DNA, leading to a 1:3 ratio of heavy to light viral DNA.

To Follow Up on Your Previous Experiment with DNA Replication