Question

A Meselson-Stahl experiment is performed on DNA isolated from an alien. How many bands would be expected to form after THREE generations, assuming a DISPERSIVE mode of DNA replication?

-one band of heavy density
-one band of intermediate density
-one band of light density
-two bands: one intermediate and one light
-two bands: one intermediate and one heavy

Answer 1

After three generations of dispersive replication of DNA, one would expect a single band with a more uniformly intermediate density, representing a mixture of older and newer DNA segments, rather than distinct heavy or light bands.

Step-by-step explanation:

If a Meselson-Stahl experiment is performed on DNA that replicates in a dispersive mode, the expected outcome after three generations would typically be multiple bands with a mix of intermediate densities. However, since the Meselson-Stahl experiment itself led to the conclusion of a semiconservative replication mechanism for bacterial DNA, based on the original experiment's design, we can infer what might happen with a hypothetical dispersive replication.

If we assume that the same patterns of banding apply, and if the alien DNA replicated in a purely dispersive mode, after three generations, you would not expect to see distinct heavy or light bands but rather a continuous distribution, likely with one band that is of even more intermediate density than after one or two generations. This assumes each generation introduces a mix of old and new DNA into the strands rather than a clear old and new separation as with semiconservative replication.