= PCR controls
{c}
<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.<How can I distinguish non-template amplification (NTC) from real products? by New England Biolabs>[FAQ: target-free control reactions and differing product sizes or melt profiles]{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.
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