Question
Given below are two statements, one labeled as assertion A and the other labeled as Reason R. Choose the correct option from the codes given below.
Assertion A: Each of the two strands of the original DNA molecule serves as a template for the synthesis of a new complementary strand. The result is two DNA molecules, each composed of one old (parental) strand and one new (daughter) strand.
Reason R: During replication, the original DNA molecule is broken into fragments and each fragment is replicated. The newly synthesized DNA fragments and the original fragments are then interspersed, resulting in both strands of the daughter DNA containing a mix of old (parental) and new (daughter) DNA segments.
Code:
Options
Solution
Sol. Key concept: DNA replication is semiconservative, not dispersive.
During semiconservative replication, the two parental DNA strands separate. Each old strand acts as a template, and complementary nucleotides are joined to form a new strand. Each daughter DNA molecule consequently contains one complete parental strand and one newly synthesized strand. Assertion A is true.
Reason R instead describes the dispersive model, in which old and new DNA segments are intermixed within each daughter strand. That is not the normal mechanism of DNA replication, so R is false.
Do not confuse this with Okazaki fragments. These are newly synthesized fragments of the lagging strand and are later joined; they do not make replication dispersive. Therefore, c is correct.
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