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Forensic Magzine, June 7, 2024: A Troubleshooting Guide for Common Issues in STR Analysis

Short Tandem Repeat (STR) analysis is a foundational piece of forensic DNA profiling, offering robust and reliable genetic information for criminal investigations. However, the intricacies of the STR workflow introduce various challenges, potentially compromising the quality and reliability of the results. Here we introduce the “Perfect” STR profile, then explore the typical pitfalls encountered during STR analysis and offer practical solutions. Our aim is to help forensic scientists navigate these challenges to achieve consistent and accurate outcomes.

The “Perfect” STR Profile

STR analysis is comprised of four steps: extraction, quantification, amplification, separation and detection resulting in an STR profile. Each step must be meticulously executed to prevent errors that could skew the results. In an ideal world the resulting STR profile contains the following attributes:

  • Complete: The STR profile is complete, meaning all necessary genetic markers are amplified and identified.
  • Intra-Locus Balance: The STR profile contains good intra-locus balance, meaning peaks of each genetic marker are consistent within a certain range. No peaks should stand out amongst the range of peaks.
  • Intra-Dye Balance: During STR analysis, multiple fluorescent dyes are used to label different sets of STR markers. Each dye emits light at a specific wavelength, which is detected by the capillary electrophoresis (CE) instrument. Different dye channels correspond to different colors (wavelengths) of fluorescence. Good balance between dye channels means that the fluorescent signals from the different dyes are of comparable intensity and quality.
  • Peak Morphology: Similar to balanced peak profiles, each peak should have a similar shape.
  • Peak Height: Like peak morphology, each STR marker peak should have a peak height within an expected range.

Because there are many variables in STR analysis, a perfect STR profile is difficult to achieve. If you have had trouble with your STR analysis, you are not alone—there are many common problems at each step of the workflow, each with potential solutions to get you closer to the perfect STR profile. more

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