Question

suppose that meselson and stahl first grew cells in light nitrogen (generation 0) and switched to heavy nitrogen (n15) for two rounds of replication. if the semiconservative model of dna replication were true, what would have meselson and stahl observed in the tubes after two rounds of dna replication? choose the letter corresponding to the correct drawing below.

Explanation:

In the semiconservative model of DNA replication, when cells are first grown in light - nitrogen (Generation 0) and then switched to heavy - nitrogen (N15) for two rounds of replication, after the first round of replication all DNA molecules are of intermediate density (one old light strand and one new heavy strand). After the second round of replication, half of the DNA molecules are of intermediate density (one old light strand and one new heavy strand) and half are of heavy density (both strands are heavy). This results in two bands, one intermediate and one heavy, which corresponds to drawing b.

Answer:

D. b