Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : DNA replication is a semi-conservative process.
Reason (R) : In semi-conservative DNA replication, the two strands of DNA are separated, and each strand serves as a template for the synthesis of a new complementary strand. Therefore, each new double-stranded DNA molecule consists of one original strand and one newly synthesized strand.
In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

To test if the Reason explains the Assertion, read them together using the connector "because":
"DNA replication is semi-conservative BECAUSE when the two strands separate, each serves as a template to make a new complementary strand, resulting in new DNA molecules with one original and one new strand."
This reads as a logical, scientifically correct explanation.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule.
The mechanism of this replication is semi-conservative, meaning the parental strands are preserved and passed down directly to the next generation.

Step 2: Detailed Explanation:
Let us analyze the assertion and reason individually:
Assertion (A): "DNA replication is a semi-conservative process."
This statement is correct.
The semi-conservative model, proposed by Watson and Crick and experimentally proven by Meselson and Stahl in 1958, is the universal mechanism of DNA replication in all living organisms.
Reason (R): "In semi-conservative DNA replication, the two strands of DNA are separated, and each strand serves as a template for the synthesis of a new complementary strand. Therefore, each new double-stranded DNA molecule consists of one original strand and one newly synthesized strand."
This statement is correct.
During replication, DNA helicase unwinds the double helix, separating the two strands.
DNA polymerase then synthesizes a new complementary strand along each template strand using base-pairing rules.
As a result, each of the two newly formed double-stranded DNA molecules contains one conserved parental strand (the original template) and one newly synthesized daughter strand.
This precise molecular mechanism directly defines and explains why the replication process is termed "semi-conservative," making (R) the correct explanation of (A).

Step 3: Final Answer:
Both (A) and (R) are true, and (R) is the correct explanation of (A).
This corresponds to Option (A).