forensic biology: artifacts quiz

two types of common artifacts

biological (PCR)

technology-related

biological (PCR) artifacts

stutter

split peaks

trialleleic peaks

technology related artifacts

pull-up

dye blobs

spikes

stutter peaks are peaks that show up BLANK than the true allele

one repeat less

stutter peaks result from BLANK

strand slippage during DNA synthesis

stutter peaks typically BLANK in height compared to true allele

<15%

many labs use BLANK so that if stutters fall below a set % of the major allele they are not considered true allele

stutter filter

split peaks

incomplete 3’ A nucleotide addition by Taq DNA polymerase

split peaks can happen as a result of BLANK

too much DNA being used

trialleleic peaks

three different sized alleles observed at a single locus

trialleleic peaks may or may not be BLANK

of equal intensity

trialleleic peaks are NOT a result from a BLANK

mixture

trialleleic peaks could be due

aneuploidy (ex. Down syndrome)

mosaicism

chimerism (ex. blood transfusion)

mutations

trialleleic peaks wouldn’t be seen BLANK

all across the profile

pull-up (bleed-through)

failure of the analysis software to discriminate between the different dye colors used during the generation of the data

pull-up is observed as a BLANK

peak-beneath a peak

pull-up most often results from using BLANK

too much input DNA

dye blobs

over time the fluorescent dye tags can become detached from the primer and migrates independently through capillary

dye blobs peaks tend to be BLANK

broader

dye blobs are also observed in the BLANK

negative PCR control

dye blobs can be removed by BLANK

cleaning with spin columns prior to CE

spikes

sharp peaks of equal intensity across all dye colors

spikes are created by

air bubbles

polymer (urea) crystals

voltage fluctuations