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Extraction methods are evaluated based on their yield and the quality of results. Early studies using HLA DQ-alpha compared Chelex® 100 with traditional organic extraction methods, and demonstrated the method's suitability for forensic samples.01, 02, 04 An advantage of this method is that there are fewer tube manipulations required when compared to traditional organic extraction methods, reducing contamination risks. Automated extraction procedures will diminish this concern even further.
Read more about Other Extraction Techniques in this course.
Chelex® 100 extraction methods are performed in a harsh environment that may not be suitable for highly degraded or low-level DNA samples.07 The alkaline environment and high temperatures could further degrade the DNA, which may result in an inability to obtain results.
One study assessed DNA samples that were isolated with Chelex ® 100, stored long-term (approximately 1 year), and subjected to several freeze-thaw cycles. When these samples were characterized using STR amplification, they showed decreased signal, peak imbalance, and allelic drop out. The authors speculated that the unbuffered suspension of the DNA, coupled with multiple freeze-thaw cycles, could accelerate the degradation process of isolated DNA samples.08
DNA isolated using the Chelex® 100 extraction is denatured. This was problematic when laboratories used restriction fragment length polymorphism (RFLP) for characterization since double-stranded DNA is required (RFLP). This is no longer a concern with current STR methods.
The Chelex® 100 procedure does not include a purification step. If the sample contains inhibitors and contaminants, increasing the sample size increases their concentration, which can inhibit PCR. Some laboratories have incorporated the use of a filter unit such as a Microcon® or Centricon® prior to amplification so that some PCR inhibitors can be removed and the sample can be concentrated. Because the resin is a PCR inhibitor, it is important to ensure that when removing the supernatant, no resin is removed from the tube.09
Read more about DNA Analysis Considerations in this course.
Chelex®100 Resin Extraction Method | |
|---|---|
| Advantages | Disadvantages |
| Fast | Harsh extraction environment (pH between 10-11 and temperature approximately 100° C) |
| Simple | Potential degradation concerns for long-term storage of isolated DNA samples |
| Inexpensive | Resin remaining in extracted DNA sample can inhibit PCR process |
| No hazardous chemicals | Less effective extraction of some sample types |
| Few tube manipulations | Isolated DNA is single-stranded |
| Binds heavy metal cations | Resin loses its chelating capacity after a few hours in suspension |
| Removes some PCR inhibitors | |
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