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STR Data Analysis and Interpretation for Forensic Analysts


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Interpretation of genotypes (allele calls) is based on a pattern of peaks or bands on an electropherogram or gel. A peak or band is a visual representation of a DNA fragment.

  • In capillary electrophoresis (CE) a peak on the electropherogram rises sharply from the baseline, has smooth sides, and is symmetrical in shape.
  • For gel-based systems, a band on the gel or gel image is distinguishable from the background and defined within a gel lane.

Read more about Capillary Electrophoresis in course: Amplified DNA Product Separation.

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Gel-based systems, unlike CE, allow analysts to visually compare alleles without a software program. However, most laboratories use software programs for both CE and gel-based sizing.

The steps in data interpretation are:

  1. Assess the internal size standards (ISS)allelic ladders, and controls.
  2. Assess each sample for the presence of extraneous peaks and determine if they may interfere with the interpretation process.
  3. Assess the data from each sample.

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