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Step One
If contamination is suspected, the first step of the investigation should be to determine where the contaminant profile has arisen. In many cases, it can be traced back to a particular step in the analysis by working backwards in a step-by-step process.
It is important to compare the contaminant profiles to:
- Other samples from the same batch
- Samples from other batches processed in the same time frame
- Staff profiles
- Previously detected contaminant profiles
- Other persons involved in the collection and handling of the evidence
If the profile contains too few alleles to effectively screen against the above, consideration can be given to boosting the signal strength by using one or more of the following:
- Amplifying additional extract
- Extending the injection time
- Concentrating the extract or amplicon
- Increasing the number of PCR cycles
These troubleshooting procedures should not be used for processing, interpreting, or reporting samples unless validated by the laboratory.
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