Excessive DNA Smearing on Gel (PCR / RT-PCR Amplification Problems)

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Amplified DNA appears as broad smear rather than discrete bands, indicating degradation or over-amplification artifacts. Common causes: 1) Excessive template concentration in reaction 2) Too many PCR cycles performed (>35 cycles) 3) Thermal cycling conditions not optimized for specific thermal cycler 4) Annealing temperature too low enabling promiscuous priming 5) Primer concentration too high 6) Extension time too long for target amplicon 7) Poor DNA template quality or degradation 8) Excessive DNA loaded on gel for electrophoresis Solutions: 1) Titrate template amount to optimal concentration for your system 2) Reduce number of cycles to below 35 3) Optimize cycling conditions based on thermal cycler manufacturer recommendations 4) When using Ready-To-Go Beads, re-optimize annealing temperature; increase by 2°C to 5°C increments 5) Titrate primer concentration to optimal level 6) Decrease extension time in small increments 7) Use freshly prepared DNA or isolate template by alternative purification method 8) Re-run gel electrophoresis with reduced sample loading volume