PCR protocol fundamentals—hands-on operation guide

critical

No PCR Product Detected

Gel electrophoresis shows no visible band at the expected product size after PCR amplification, indicating complete reaction failure.

💡 8 · ✓ 8

severe

No Band or Faint Band Due to Reagent Concentration Issues

Gel shows no amplification product or very weak bands despite correct thermal cycling parameters, indicating problems with reaction component concentrations.

💡 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

No Band or Faint Band with GC-Rich Templates

PCR fails or produces very weak amplification specifically with high GC content templates (>65%). Standard protocols work with other templates but not GC-rich sequences.

💡 3 · ✓ 4

severe

No Product Due to Suboptimal Cycling Parameters

No amplification product visible despite proper template and reagents, suggesting thermal cycling conditions are inappropriate.

💡 4 · ✓ 4

severe

Sequence Errors Within PCR Product Body

Sequencing reveals point mutations, insertions, or deletions within the amplified fragment that are not present in original template.

💡 5 · ✓ 6

moderate

Incorrect Reaction Efficiency Due to Oligo Binding to Non-Molecular Biology Tubes

Variable and incorrect standard curve efficiency when using serial dilutions; effect more pronounced when same dilution series stored at 4°C and reused; inconsistent differences between amplification plots; problem resolves when different operator uses different tubes

💡 4 · ✓ 5

moderate

Nonspecific Bands or Primer-Dimers

Multiple bands appear on gel in addition to or instead of the expected target band. Primer-dimer artifacts or nonspecific amplification products are visible, indicating lack of reaction specificity.

💡 7 · ✓ 7

moderate

Smeared Bands Due to Excessive Thermal Cycling

Gel shows smeared or diffuse bands rather than discrete sharp bands. The smearing pattern suggests heterogeneous product populations from excessive amplification or nonspecific priming.

💡 6 · ✓ 6

moderate

Nonspecific Bands or Primer-Dimers Due to Thermal Cycle Issues

Gel shows multiple bands instead of single target band, or primer-dimers appear as small molecular weight products. The desired product may be present but accompanied by unwanted amplification artifacts.

💡 6 · ✓ 6

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