DNA Analysis & Interpretation Flashcards
7 cards from real CFC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 DNA Analysis & Interpretation flashcards as text
Which quality assurance standard governs accredited forensic DNA laboratories in the United States?
Answer: FBI Quality Assurance Standards (QAS) for Forensic DNA Testing Laboratories
The FBI's Quality Assurance Standards for Forensic DNA Testing Laboratories set mandatory requirements for all laboratories submitting profiles to CODIS.
What is the purpose of a 'negative control' in a forensic DNA amplification run?
Answer: To detect contamination by showing no DNA amplification in the absence of a sample
A negative control contains all reagents except a DNA template; any amplification signals contamination of the reagents or process.
In probabilistic genotyping, what does a likelihood ratio (LR) greater than 1 indicate?
Answer: The evidence is more likely if the suspect contributed than if an unknown person did
An LR > 1 means the observed DNA evidence is more probable under the prosecution hypothesis (suspect contributed) than the defense hypothesis (unknown contributor).
A forensic DNA laboratory receives a reference swab and a crime scene sample. Before comparison, the analyst confirms the samples were collected and stored separately. Why is this critical?
Answer: To prevent contamination and ensure the reference did not inadvertently transfer DNA to the evidence sample
Separate handling and storage of reference and evidence samples prevents cross-contamination that could create a false association.
Which forensic scenario is best addressed by familial DNA searching in a CODIS database?
Answer: Identifying an unknown suspect through a close relative whose profile is in CODIS
Familial searching looks for partial matches in CODIS that may indicate a close biological relative of the unknown contributor, potentially leading to an unidentified suspect.
What does 'peak height ratio' (PHR) indicate in STR analysis, and what threshold commonly triggers concern?
Answer: The relative height of two alleles at a heterozygous locus; imbalance below 60-70% may indicate dropout or mixture
PHR compares allele peak heights at heterozygous loci; ratios below laboratory thresholds (typically 60-70%) may indicate allelic dropout or suggest a mixture.
A defense attorney challenges a DNA match by arguing that databases used for statistical calculations don't represent the defendant's ethnic group. What is the most scientifically appropriate response?
Answer: Use the population database most representative of the defendant's ethnic group and apply the NRC II recommendations, including the ceiling principle if needed
NRC II guidelines recommend using the most relevant population database and applying conservative corrections such as the ceiling principle to address database limitations.