PCR protocol fundamentals—hands-on operation guide

critical

No Band Due to Incorrect Component Concentrations

No visible band or very faint band on gel despite proper thermal cycling parameters. The reaction components may be at suboptimal or inhibitory concentrations.

💡 5 · ✓ 5

critical

No Band or Faint Band Due to Incorrect Component Concentrations

PCR amplification fails or produces very weak bands. Thermal cycling parameters appear correct, but reaction components may be improperly balanced or missing.

💡 6 · ✓ 6

critical

Complete Absence of PCR Product

No bands visible on agarose gel after PCR amplification, indicating complete reaction failure.

💡 6 · ✓ 6

critical

No Band Due to Omitted Critical Components

Complete absence of PCR product on gel due to missing essential reaction components, representing a critical setup error.

💡 5 · ✓ 5

severe

No Band or Faint Band Due to Thermal Cycling Errors

No visible band or very faint band appears on the gel after PCR amplification. This indicates insufficient or failed amplification of the target sequence.

💡 6 · ✓ 6

severe

No Band or Faint Band Due to Suboptimal Thermal Cycling Parameters

No visible PCR product band appears on the gel, or only a very faint band is detected. This occurs despite using appropriate template and primers, suggesting insufficient amplification.

💡 6 · ✓ 6

severe

Insufficient Amplification from Polymerase Issues

Weak or absent PCR product. Primers are degraded or show primer-dimer formation at the bottom of gel.

💡 4 · ✓ 5

severe

Sample Fails to Amplify Despite Positive Control Success

Positive control amplifies successfully but test sample known to contain target shows no amplification; undiluted template fails while dilutions may show improved amplification

💡 3 · ✓ 5

severe

Assay Failure When Switching Master Mix Products

Previously working assay fails completely when switching to different master mix brand; positive controls fail; original master mix works but new one does not despite similar specifications

💡 4 · ✓ 5

severe

Sequence Errors in PCR Product

Sequencing of the PCR product reveals mutations, insertions, deletions, or other sequence variations compared to the original template DNA.

💡 6 · ✓ 6

moderate

No Band or Faint Band Due to Template Quality Problems

PCR fails or produces weak products despite correct reagent concentrations and cycling parameters, due to compromised template DNA quality or presence of inhibitors.

💡 4 · ✓ 4

moderate

Smeared Bands on Gel

PCR products appear as continuous smears rather than discrete bands on gel, indicating template degradation, excessive cycling, or nonspecific amplification throughout a size range.

💡 5 · ✓ 5

moderate

PCR污染和携带污染

Unexpected products appear in negative controls or multiple samples show identical non-specific bands, indicating contamination from previous amplifications or environmental sources.

💡 4 · ✓ 7

moderate

Excessive DNA Smearing on Gel

Amplified DNA appears as broad smear rather than discrete bands, indicating degradation or over-amplification artifacts.

💡 8 · ✓ 8

moderate

Amplification Failure from Suboptimal Cycling Parameters

No product or very weak bands despite proper template and primer quality. Reaction components appear functional in other assays.

💡 4 · ✓ 4

moderate

JumpStart Taq ReadyMix Underperforming Due to Incorrect Hot Start Protocol

JumpStart Taq ReadyMix does not work as well as similar products from different suppliers; amplification is weak or absent despite correct assay design

💡 3 · ✓ 3