Step-by-Step PCR Experiment Protocol Guide

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

No PCR Product (Complete Failure)

No bands visible on gel electrophoresis after PCR amplification

💡 10 · ✓ 10

critical

False Positive PCR Results from DNA Contamination

No-template controls (NTC) or negative controls show unexpected amplification. Particularly problematic in sensitive applications like human identification qPCR where trace DNA contamination produces false positives.

💡 3 · ✓ 3

severe

Unexpected PCR Product

PCR produces a band of incorrect size or sequence not matching the expected target

💡 5 · ✓ 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

Nonspecific Amplification Products

Extra, unwanted bands appear on gel in addition to or instead of the target product, indicating off-target amplification.

💡 6 · ✓ 6

severe

No or Low PCR Amplification Due to Plastic Consumable Issues

PCR reaction fails to produce expected amplification or yields significantly reduced product, despite optimized reagents and cycling parameters. The issue traces to suboptimal thermal transfer or contamination from the plastic vessel itself.

💡 4 · ✓ 4

severe

Plate or Tube Melting and Adhering to Block

After PCR program completion, plates or tubes are found melted or stuck to the thermal cycler block, making removal difficult and potentially damaging samples. Plastic shows signs of thermal degradation.

💡 3 · ✓ 3

severe

PCR Sample Evaporation and Loss During Cycling

Visible reduction in reaction volume after thermal cycling, with condensation on tube caps or film. May result in concentrated reagents, failed reactions, or inability to recover product.

💡 3 · ✓ 3

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

Low PCR Product Yield

Desired PCR fragment appears faint or barely visible on gel electrophoresis

💡 14 · ✓ 14

severe

GC-Rich Template Amplification Failure

PCR fails to amplify templates with high GC content or produces very low yields

💡 5 · ✓ 8

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

Variable qPCR Data Across Wells

Quantitative PCR shows inconsistent Cq values or fluorescence intensities between technical replicates in different wells, despite identical reaction setup. Well-to-well variability exceeds acceptable coefficient of variation.

💡 2 · ✓ 2

moderate

PCR Tube Crushing or Deformation Under Lid Pressure

PCR tubes become crushed, collapsed, or deformed after thermal cycling, potentially causing sample loss or compromised seal integrity. Tubes may show visible damage especially when using tube strips.

💡 3 · ✓ 3

moderate

PCR Tube Caps Popping Off During Cycling

Individual tube caps become dislodged during thermal cycling, exposing samples to evaporation and potential contamination. Caps are found loose or completely separated from tubes after run completion.

💡 3 · ✓ 3

moderate

Nonspecific Bands in PCR

Multiple unwanted bands appear on gel electrophoresis alongside or instead of the desired PCR product

💡 4 · ✓ 5

moderate

PCR Product Smearing on Gel

Gel electrophoresis shows smeared or streaked bands instead of distinct sharp bands

💡 6 · ✓ 7

moderate

Primers Stop Working Over Time

Primers that initially worked successfully for PCR gradually fail or produce poor results after storage

💡 4 · ✓ 5

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

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

moderate

Pressure-Sensitive Film Not Adhering to Plate

Sealing film peels away from plate wells either before or during thermal cycling, leading to sample evaporation or cross-contamination. Film appears to have poor bonding with well rim surfaces.

💡 2 · ✓ 2

minor

High Molecular Weight Material Stuck in Wells

Ethidium bromide-stainable material remains in the gel wells and does not migrate during electrophoresis

💡 3 · ✓ 4