Question

Given below are two statements: One is labelled a Assertion (A) and the other is labelled as Reason(R)

Assertion (A): Semiconservative replication wa experimentally proved by Mathe Meselson and Franklin Stahl (1958)
Reason (R): Meselson and Stahl used radioactiv isopope 15 N and equilibrium densit gradient centrifugation technique.

In the light of the above statements, choode the correct answer from the optionsgiven below:

A. Both (A) and (R) are true and (R) is not the correc explanation of (A).
B. (A) is true but (R) is false.
C. (A) is false but (R) is true.
D. Both (A) and (R) are true and (R) is the correc explanation of (A).

Answer 1

The assertion (A) and reason (R) are both true, and (R) is the correct explanation of (A) because Meselson and Stahl's foundational experiment used 15N labeling and density gradient centrifugation to demonstrate the mechanism of semiconservative DNA replication.

Step-by-step explanation:

The work of Matthew Meselson and Franklin Stahl in 1958 crucially demonstrated that DNA replication is semiconservative. They used a heavy isotope of nitrogen, 15N, to label DNA and then observed the distribution of this label after DNA replication in a lighter 14N medium. The use of equilibrium density gradient centrifugation allowed them to observe the densities of the DNA molecules after replication. Their experiment revealed that DNA after one generation in 14N medium was of intermediate density, thus supporting the semiconservative model. After a second generation, the presence of two bands of DNA, one of intermediate and one of light density (14N), confirmed that DNA replication is indeed semiconservative.

Therefore, the correct answer to the original question is: Both (A) and (R) are true and (R) is the correct explanation of (A).