Template requirements in PCR — Under standard DNA PCR (not RT-PCR), which nucleic acid template is used for amplification?

Introduction / Context:
PCR amplifies specific DNA sequences using cycles of denaturation, primer annealing, and extension. Clarifying what nucleic acid serves as the template in standard PCR (as opposed to reverse-transcription PCR) helps avoid common laboratory errors and misinterpretations.

Given Data / Assumptions:

• The question refers to conventional DNA PCR, not RT-PCR.
• Primers are DNA oligonucleotides that anneal to complementary DNA sequences.
• Thermocycling includes an initial denaturation step to separate strands.

Concept / Approach:
Standard PCR uses double-stranded DNA (dsDNA) as the starting template. The first denaturation step separates the two strands, producing single-stranded regions for primer binding. Although PCR can, in principle, amplify from single-stranded DNA if a primer can anneal, the canonical and routinely used template is dsDNA. RNA templates require an additional reverse transcription step to generate complementary DNA (cDNA) for amplification (RT-PCR), and therefore are not the direct template in standard PCR.

Step-by-Step Solution:

Verification / Alternative check:
Protocol manuals specify an initial denaturation of dsDNA templates prior to cycling, confirming the routine use of dsDNA.

Why Other Options Are Wrong:

• RNA: requires reverse transcription first (RT-PCR).
• Single-stranded DNA: possible but not the standard template described in basic PCR methods.
• None of these: incorrect because dsDNA is correct.

Common Pitfalls:
Confusing RT-PCR (RNA → cDNA → PCR) with DNA PCR; always verify the nature of the input nucleic acid.

Final Answer:
double stranded DNA