PCR inhibitor
Definition
A substance in a sample extract that suppresses the polymerase chain reaction, reducing amplification efficiency or causing amplification failure. Haemoglobin, melanin, humic acids from soil, and some cleaning agents are common inhibitors in biological evidence extracts.
- Common sources in biological evidence
- Haemoglobin, melanin, humic acids from soil, cleaning agents
- Common sources in wildlife products
- Tannins, polyphenols, bile acids, residual processing chemicals
- Mechanism
- Blocks Taq polymerase or degrades primers, reducing or halting DNA amplification
Common questions
What are PCR inhibitors and where do they come from?+
PCR inhibitors are substances that block or reduce the polymerase chain reaction, preventing DNA from being amplified properly. They come from many sources. Biological samples contain haemoglobin and melanin. Soil has humic acids. Wildlife products carry tannins, polyphenols, bile acids, and processing chemicals left behind during manufacturing.
How do PCR inhibitors damage the DNA test?+
They work by blocking Taq polymerase (the enzyme that copies DNA) or by breaking down primers (the DNA markers that start amplification). Either way, the result is partial amplification failure or complete failure. A sample that should produce a clear DNA profile can become unreadable.
Why does it matter in forensic labs?+
PCR inhibitors are a routine headache for DNA extraction from biological evidence and wildlife samples. Labs have to recognize when inhibition is occurring and clean up extracts before they waste time and reagents on failed amplification.
Related terms
- Chain of custody
- The unbroken documentary trail of who held a sealed exhibit, when, and under what seal, from the moment of collection through analysis...
- Collagen peptide barcoding
- Species identification from trypsin-digested collagen analysed by mass spectrometry. Peptide sequences differ between species at diagnostic positions that survive tanning and heat...
- Destructive testing
- Any test that consumes, extracts, or chemically alters the stain material: cutting a fabric swatch, swabbing a surface, adding a chemical reagent....
- Differential extraction
- A DNA extraction method used for sexual assault evidence that separates sperm cells from epithelial cells before cell lysis, yielding two DNA...
- DNA fragmentation
- Physical breakage of the DNA backbone into short pieces. In degraded samples the average fragment length may be 50-200 bp, making long...
- Library preparation (aDNA)
- Enzymatic end-repair, adapter ligation, and amplification of all DNA fragments in a sample regardless of length, used in ancient-DNA and degraded-sample workflows....
- Metagenomics
- Shotgun sequencing of all DNA in a sample followed by bioinformatic assignment of reads to taxa. Does not require prior knowledge of...
- Non-destructive examination
- Any examination that does not consume or significantly alter the stain: visual inspection, alternate light source (ALS) examination, photography, and microscopy of...
- Sequential testing protocol
- The standardised order in which biological stains are examined: presumptive test, then confirmatory test, then species confirmation, then typing and DNA analysis....
- Short-amplicon strategy
- A PCR design that targets the shortest possible fragment length: often 80-150 bp: within a diagnostic locus such as COI. Shorter targets...
Explained in these topics
- DNA from Degraded and Processed Wildlife ProductsA compound co-extracted with DNA that blocks Taq polymerase or degrades primers. Common inhibitors in wildlife products include tannins, polyphenols, bile acid...
- Order of Testing and DNA PreservationA substance in a sample extract that suppresses the polymerase chain reaction, reducing amplification efficiency or causing amplification failure. Haemoglobin,...