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 CONSERVATIVE mode of DNA replication?

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

Answer 1

The Meselson-Stahl experiment demonstrated that DNA replication occurs in a semi-conservative manner. After one generation of growth in a medium containing 14N, a single band of intermediate density was observed, ruling out the conservative mode of replication. After three generations, we would expect to see two bands: one intermediate and one light.

Step-by-step explanation:

The Meselson-Stahl experiment is a classic experiment that demonstrated that DNA replication occurs in a semi-conservative manner. In a conservative mode of replication, the original DNA molecule would remain intact and form one band of heavy density, while a newly synthesized molecule would form another band of light density. However, the experiment showed that after one generation of growth in a medium containing ¹4N, a single band of intermediate density was observed, ruling out the conservative mode. After three generations, assuming a conservative mode of replication, we would expect to see two bands: one intermediate and one light. Therefore, the correct answer is two bands: one intermediate and one light.