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DNA Extraction and Quantitation for Forensic Analysts


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Current forensic DNA analysis uses polymerase chain reaction (PCR) based short tandem repeat (STR) testing. Many laboratories use commercially available STR amplification kits. Depending on the kit and reaction volume, the optimal concentration of input DNA will be in the range of 0.5ng – 2ng. Adding too much or too little DNA to the amplification reaction can result in problems in the analysis.

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

n addition to the need for amplification optimization, quantitation of the amount of human DNA present in samples is a requirement of the QAS.

The quantitation process also serves as a quality control and/or troubleshooting procedure. If the STR results are not concordant with those from the quantitation, it may be an indication of a problem, such as inhibition, sample switching, or contamination.


Historical and commonly used quantitation methods include the following:

  • Yield gels
  • Spectrophotometry
  • Fluorometry
  • Slot blot hybridization
  • AluQuant®
  • Quantitative PCR (qPCR)

Quantitative PCR is the most widely used technique today

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