First-person PCR and gel electrophoresis demonstration

critical

Complete Absence of PCR Product

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

💡 6 · ✓ 6

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

Incorrect PCR Product Size

Gel electrophoresis shows PCR product band(s) at unexpected molecular weight, either larger or smaller than the predicted amplicon size.

💡 3 · ✓ 4

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

moderate

Nonspecific Bands or Primer-Dimers Due to Component Imbalance

Multiple bands or primer-dimers appear on gel despite optimized thermal cycling. Component concentrations may be promoting nonspecific primer interactions or amplification.

💡 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

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 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