First-person PCR and gel electrophoresis demonstration

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 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

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

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

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

Primer Dimer Formation

Small molecular weight band (typically 50-100 bp) visible at bottom of gel, representing primer self-amplification artifacts that compete with target amplification.

💡 3 · ✓ 4

moderate

Nonspecific Amplification and Smearing on Gel

Gel shows multiple bands, smears, or high background instead of single clean product band. May include primer-dimers at bottom of gel.

💡 6 · ✓ 6

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

Nonspecific Bands or Primer-Dimers Due to Reagent Issues

Multiple unwanted PCR products appear on gel alongside or instead of target band, caused by reagent concentration imbalances or primer design problems.

💡 4 · ✓ 4

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