PCR specificity

PCR specificity concerns whether the accumulated amplicon comes from the intended interval. Binding temperature, PCR primer nucleotide sequences and their possible alternative binding sites matter. Too permissive binding can support competing products; excessively restrictive binding can prevent the intended product. A band of the expected length is useful evidence, but unrelated nucleotide sequences can have the same length. DNA sequencing tests identity more directly, subject to mixtures and copying errors.^[ref]

A primer dimer is an amplification artifact in which PCR primers provide extendible partners for one another. Its accumulation consumes substrates and may produce a signal even without the intended template. It is not evidence that the intended amplicon was present.^[ref]

PCR controls are scientific controls that separate different explanations for a readout. A no-template reaction contains the PCR primers and copying reagents but replaces the added template with water or sample buffer. Amplification there can indicate carried-over DNA or a primer dimer; a clean result does not exclude contamination confined to one sample.^[ref]

Different comparisons answer different questions. A known amplifiable template tests whether the PCR primers, DNA polymerase and thermal cycler can produce the expected amplicon. An extraction blank follows sample preparation without adding the sampled material. A separate amplifiable interval in the sample can test whether recovered DNA supports copying, although success there does not guarantee success at the target. A length standard calibrates gel electrophoresis; it is not a control for the copying reaction. These comparisons are an analytical design extension to the teaching example below, not a claim that its student protocol includes every comparison.