Scenario
The expected band is weak and the sample lane shows broad smearing.
The goal is to avoid blaming PCR immediately when loading amount, salt, degraded template, or voltage may explain the pattern.
Inputs to confirm
DNA amount loaded per lane.
Gel percentage and running voltage.
Whether the ladder and controls separated normally.
How to use the result
First confirm whether the gel system behaved normally using the ladder and controls.
If only one sample smears, review sample quality and loading amount before changing the entire PCR program.
Common failure points
Overloading a lane and interpreting the smear as template degradation.
Using the wrong gel percentage for the expected size range.
Running too hot and distorting bands across the gel.