PCR Inhibitor
Definition
A co-extracted substance that interferes with Taq polymerase activity or primer annealing. Common inhibitors in forensic samples include haemoglobin (from blood on cloth), humic acids (from soil), collagen (from bone), and melanin (from hair). Inhibition can cause partial profiles even when DNA quantity is adequate.
- 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
- Differential Extraction
- A two-step DNA extraction procedure used when a stain contains both sperm cells and non-sperm epithelial cells. The first step lyses epithelial...
- 8-Oxoguanine
- An oxidised form of guanine produced by reactive oxygen species attacking the C8 position of the guanine ring. 8-Oxoguanine mispairs with adenine...
- Abasic Site
- A position in the DNA backbone where the nitrogenous base has been lost, leaving only the deoxyribose-phosphate scaffold. Also called an AP...
- Chain of Custody
- The documented chronological record of who collected, handled, transferred, and examined a piece of evidence. For digital evidence, chain of custody includes...
- Chelex Extraction
- A rapid extraction method that uses the chelating resin Chelex 100 to bind divalent metal ions and prevent nuclease activity. Cells are...
- 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...
- Depurination
- Hydrolytic cleavage of the N-glycosidic bond between deoxyribose and a purine base (adenine or guanine), generating an abasic (apurinic) site. Abasic sites...
- Destructive Testing
- Any test that consumes, extracts, or chemically alters the stain material: cutting a fabric swatch, swabbing a surface, adding a chemical reagent....
- 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...
- Internal Positive Control (IPC)
- An exogenous DNA template of known sequence and concentration added to the PCR reaction alongside the forensic sample. If the IPC fails...
- 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
- The direct sequencing of all DNA extracted from an environmental sample, bypassing the need to culture individual organisms. It produces a community-wide...
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...
- DNA Degradation: Mechanisms, Inhibitors and Environmental EffectsAny substance that, when co-purified with DNA and carried into a PCR reaction, reduces or abolishes amplification. Inhibitors act by several mechanisms: chelat...
- DNA Extraction and Quantification from Biological EvidenceA co-extracted substance that interferes with Taq polymerase activity or primer annealing. Common inhibitors in forensic samples include haemoglobin (from bloo...
- 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,...