artifacts Flashcards
OLA / OMR
OLA - off ladder allele; recognized alleles that are located in red ‘bins’
OMR - outside marker range; allele that is calling outside of locus (not in grey or red ‘bins’)
Tri-allele
three-peak pattern exhibited at a locus of a single source contributor
Stutter
minor peak typically observed one repeat unit shorter than primary peak (sometimes one repeat unit longer) - caused by strand slippage of Taq polymerase during PCR extension when the primer-template complex becomes unpaired
Split peaks (-A)
if PCR is ended before the completion of adenylation, an amplicon is created which is one base pair shorter than the true peak - often occurs in samples with too much template DNA
Non-specific amplification
when PCR primers anneal to template sequences that are not perfectly complementary - this newly synthesized region then acts as a template for primer extension and synthesis of undesired amplification products
Null alleles
an allele that is present in the sample yet is not amplified - often caused by a primer binding site mutation
Migration issues
a fragments migrating at different rates between injections on the same run/plate - most often this results in multiple OL’s, especially toward right side of egram at larger molecular weight loci
Spikes
caused by an electrical impulse during injection
Dye blobs
free fluorescent dye molecules that coexist with dye-labeled primers and are injected and separated during electrophoresis
Formamide blobs
when formamide decomposes into formate - formate is injected preferentially into capillary causing loss of signal intensity
Pull-up peaks
peak signal that carries over to an adjacent color channel - approximately < 3% of parent peal
Size standard failure
loss of resolution in size standard (aka peak broadening) - oversaturation of CCD camera caused by off-scale data
