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STR Data Analysis and Interpretation for Forensic Analysts

Non-Template Addition

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Image of Non-Template Addition
National Institute of Justice (NIJ) (see reuse policy).

If too much input DNA is added to an amplification reaction, the polymerase may be unable to complete the extension for all amplicons.03 Non-template addition results in a PCR (Polymerase Chain Reaction) product that is one base pair longer than the actual target sequence. When the polymerase is unable to complete the adenine addition on all products, this results in what is commonly referred to as split peaks (+A/-A peaks).01 To minimize split peaks, the extension phase of the PCR process is designed to drive the addition of adenine, ensuring that all amplicons are the same length. Kit manufacturers have also developed primer sequences that encourage adenine addition.

Read more about PCR in course: Crime Scene and DNA Basics for Forensic Analysts.


Samples displaying -A can be diluted with buffer and reextended in the thermal cycler.

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