STR Interpretation 1

STR Interpretation 1 - Allelic Ladder STR Analysis is Performed by Comparing Size of Questioned Peak to Allelic Ladders Variant allele Outline z

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Allelic Ladder STR Analysis is Performed by Comparing Size of Questioned Peak to Allelic Ladders Variant allele Outline g What are STRs and how are they amplified g STR applications in forensics – Capillary electrophoresis – Analysis of DNA data using Genemapper g STR analysis and interpretation issues – Case examples g Additional STR applications – Y Chromosome STRs Practical Considerations Regarding DNA Data Analysis g Stutter g -A/+A g Amplification locus imbalance g Pull-up g Degraded template g Is it a real peak? – Stochastic fluctuation, spikes, rfu thresholds, and minor peaks g Mixture interpretation g Primer binding microvariants Stutter Stutter – a reproducible characteristic of Taq activity. ….not an “artifact”. Stutter is the result of repeat slippage during the primer extension step of PCR. Mechanism: Taq polymerase can stall and fall off during DNA synthesis. The extended stand breathes apart and can reanneal out of register. The most common result is a minor peak at N-4 base pairs. RFU 100 104 Size (bp) Stutter is common. Observed at most STR loci used in forensic testing. Peaks are identified as stutter based on validation studies: testing known samples (empirically define stutter percentage or “stutter cut-offs”). --by the kit manufacturer --by the user laboratory Stutter Characteristics General trends: G Larger amplification products have higher stutter percentage. -Locus to locus: generally more stutter is observed at larger loci. -Within a locus: larger alleles usually have more stutter.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Case Sample with Stutter Real peaks Below Stutter Threshold 5-fold fold more product 10% 10% Actual Actual % stutter % stutter is the same is the same Threshold Threshold of detection of detection is exceeded is exceeded for main peak for main peak
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 09/21/2009 for the course MCB 3416 taught by Professor Ladd during the Fall '08 term at UConn.

Page1 / 6

STR Interpretation 1 - Allelic Ladder STR Analysis is Performed by Comparing Size of Questioned Peak to Allelic Ladders Variant allele Outline z

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online