During which DNA-related process do both strands of the parental DNA act as templates at the same time, yielding two daughter duplexes (leading and lagging synthesis coordinated at a replisome)?

Introduction / Context:
Cells must duplicate their genomes before division. Semi-conservative replication uses each parental strand as a template to build a complementary daughter strand, producing two identical duplex molecules. At the replication fork, synthesis on both templates is coordinated by a multi-enzyme replisome.

Given Data / Assumptions:

• Replication forks generate leading and lagging strands.
• Leading strand: continuous 5'→3' synthesis.
• Lagging strand: discontinuous 5'→3' synthesis (Okazaki fragments) with RNA priming.

Concept / Approach:
In replication, both templates are copied simultaneously: one continuously, one discontinuously. Repair pathways (excision, mismatch) typically excise and resynthesize short patches on one strand rather than duplicating the entire chromosome concurrently from both templates.

Step-by-Step Solution:
Identify the process that necessarily uses both strands as templates across long regions: replication.Contrast with repair pathways that replace limited tracts, not full duplex duplication.Select replication as correct.

Verification / Alternative check:
Meselson–Stahl experiments demonstrated semi-conservative replication: each daughter duplex contains one old and one new strand, proving both parental strands serve as templates.

Why Other Options Are Wrong:

• Excision/mismatch repair: template choice is local and patch-based; not simultaneous full-strand copying.
• “None”: incorrect because replication precisely fits the description.

Common Pitfalls:
Assuming “both strands” implies bidirectional repair; in reality, only replication mandates long, coordinated synthesis on both templates at forks.

Final Answer:
Replication