Allelic Ladder
Definition
A multi-allele reference standard containing the full range of known alleles at each STR locus in the panel, co-injected with samples to allow allele designation by size comparison.
- Contents
- Full known allele range per STR locus
- Function
- Size-based allele designation reference
- Injection timing
- Co-run with every sample batch
- Example kits
- GlobalFiler, PowerPlex Fusion
Common questions
Why must the ladder be run with every batch instead of reused from calibration?+
Capillary electrophoresis migration times drift slightly between runs due to temperature, polymer batch, and instrument condition, so an allele call is only valid relative to a ladder injected in the same run. This run-specific sizing is what lets analysts assign an exact repeat number rather than an approximate fragment size.
What does it mean if a ladder peak is missing or distorted in a run?+
A degraded ladder profile invalidates allele calls for that injection because the size standard the software relies on is incomplete, so the run is typically flagged and repeated rather than interpreted.
Related terms
- 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...
- 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...