Step-by-Step PCR Experiment Protocol 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

No PCR Product (Complete Failure)

No bands visible on gel electrophoresis after PCR amplification

💡 10 · ✓ 10

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

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 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 Due to Template or Reagent Quality Issues

PCR fails to produce visible band despite correct concentrations and cycling parameters. Template degradation, contamination, or impure reagents may be inhibiting the reaction.

💡 5 · ✓ 5

severe

No Band or Faint Band Due to Thermal Cycling Issues

After PCR amplification and gel electrophoresis, no visible band appears at the expected product size, or only a very faint band is observed, indicating insufficient or failed amplification.

💡 6 · ✓ 6

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 Due to Primer Design or Quality Issues

No PCR product is obtained despite correct thermal cycling and component concentrations. Investigation reveals potential primer-related issues including design flaws or contamination.

💡 5 · ✓ 5

severe

Multiple or Non-Specific PCR Products

Gel electrophoresis reveals multiple bands, smearing, or bands at incorrect sizes in addition to or instead of the expected product, indicating lack of amplification specificity.

💡 7 · ✓ 7

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

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

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

No Product Due to Suboptimal Cycling Parameters

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

💡 4 · ✓ 4

moderate

Smeared Bands Due to Template Quality or Concentration Issues

Gel displays smeared bands suggesting degraded products or heterogeneous amplification. Template-related issues such as degradation, contamination, or excessive concentration are suspected.

💡 6 · ✓ 6

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

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

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

Irregular Standard Curve Spacing Due to Sample Inhibitors

Cq data for standard curve dilutions are irregularly spaced; ΔCq between dilutions is inconsistent and decreases with increasing dilutions; replicates are precise but pattern is abnormal

💡 3 · ✓ 5