Pull-Up (Bleed-Through)
Definition
A spectral artefact where a tall peak in one dye channel generates a spurious smaller peak in an adjacent dye channel at the same size, due to incomplete spectral matrix correction.
- Domain
- Capillary electrophoresis, DNA STR typing
- Cause
- Incomplete spectral matrix correction between dye channels
- Effect
- Spurious peak in an adjacent dye channel at the same size
Common questions
How is pull-up told apart from a true minor allele?+
A pull-up peak appears at the exact fragment size of the tall parent peak, is proportional in height to it, and shrinks or disappears after the instrument's spectral matrix or colour separation is recalibrated.
Why does an unrecognised pull-up peak matter for mixture interpretation?+
It can be mistaken for a genuine minor contributor allele, artificially inflating perceived mixture complexity or leading to the false inclusion or exclusion of a contributor.
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...
- 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...
- Stutter Peak
- A PCR artefact appearing one repeat unit below (and occasionally above) a genuine allele peak, caused by polymerase slippage. Typically 5-15% of...