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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.
Methods
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
Additional Online Courses
- What Every First Responding Officer Should Know About DNA Evidence
- Collecting DNA Evidence at Property Crime Scenes
- DNA – A Prosecutor’s Practice Notebook
- Crime Scene and DNA Basics
- Laboratory Safety Programs
- DNA Amplification
- Population Genetics and Statistics
- Non-STR DNA Markers: SNPs, Y-STRs, LCN and mtDNA
- Firearms Examiner Training
- Forensic DNA Education for Law Enforcement Decisionmakers
- What Every Investigator and Evidence Technician Should Know About DNA Evidence
- Principles of Forensic DNA for Officers of the Court
- Law 101: Legal Guide for the Forensic Expert
- Laboratory Orientation and Testing of Body Fluids and Tissues
- DNA Extraction and Quantitation
- STR Data Analysis and Interpretation
- Communication Skills, Report Writing, and Courtroom Testimony
- Español for Law Enforcement
- Amplified DNA Product Separation for Forensic Analysts