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STR Data Analysis and Interpretation for Forensic Analysts

Step 2: Extraneous Peaks

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The second step is to assess each sample to determine if there are any extraneous peaks, and if they interfere with the interpretation process. Extra peaks within an allele range should be assessed following laboratory procedures.

Read more about Extraneous Peaks in this course.


Various artifacts can complicate and/or interfere with the interpretation process. Prior to interpreting allele designations, the analyst should evaluate each sample to determine if artifacts are present. All samples, to include controls and ladders, should be assessed for the following:

  • Stutter
  • 3'-A nucleotide addition
  • Spurious peaks (spikes, blobs, noise)
  • Pull-up

If any of these artifacts are present, the analyst should follow the procedures established by the laboratory.

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