Stutter Peak
Definition
A PCR artefact appearing one repeat unit below (and occasionally above) a genuine allele peak, caused by polymerase slippage. Typically 5-15% of the parent allele height.
- Cause
- Polymerase slippage during PCR
- Position
- One repeat unit below parent allele
- Typical height
- 5 to 15 percent of parent peak
- Platform
- Capillary electrophoresis
Common questions
How do examiners distinguish a stutter peak from a true minor contributor?+
Laboratories set locus-specific stutter thresholds from validation data, and a peak at the n-1 position is treated as stutter, not a true allele, if its height falls within the expected percentage of the parent peak rather than exceeding it.
Why does stutter threshold matter for interpreting DNA mixtures?+
In a mixed sample, a genuine low-level contributor's allele can fall at the same position as expected stutter, so an incorrectly set threshold risks either masking a real contributor or wrongly treating an artefact as evidence of an additional person.
Related terms
- Allelic Ladder
- A multi-allele reference standard containing the full range of known alleles at each STR locus in the panel, co-injected with samples to...
- Capillary Electrophoresis (CE)
- A separation technique that resolves DNA fragments by size through a polymer-filled glass capillary under an applied electric field. Single-base resolution is...
- Drop-in
- Sporadic appearance of a low-level peak not reproducibly present in re-amplifications, typically caused by trace contamination. Distinguished from genuine minor-contributor alleles by...
- Drop-Out
- Failure of a genuine allele to amplify above the analytical threshold, typically due to low or degraded template. Creates apparent homozygosity at...
- GeneMapper ID-X
- Applied Biosystems analysis software for STR genotyping. Current-generation tool used in the majority of US, UK, and Australian forensic DNA laboratories.
- OSIRIS
- Open-source STR analysis software developed by NIST (US National Institute of Standards and Technology), used as an independent or supplementary analysis tool...
- Pull-Up (Bleed-Through)
- A spectral artefact where a tall peak in one dye channel generates a spurious smaller peak in an adjacent dye channel at...
- Spectral Matrix
- A mathematical correction factor that decouples the overlapping emission spectra of the fluorescent dyes used in a multiplex STR kit. Must be...
- Stochastic Threshold (ST)
- A validated minimum peak height below which allele calls are considered uncertain due to stochastic amplification effects. Profiles with peaks between the...