CFC DNA Analysis & Interpretation 2 — Questions and Answers
Question 1: A forensic analyst obtains a DNA profile from a degraded sample with only 8 of 20 CODIS loci amplified. What is the most appropriate course of action?
- Report the partial profile as inconclusive and discard
- Compare the partial profile and note the reduced statistical weight (Correct answer)
- Request re-collection of evidence before any comparison
- Amplify additional loci using non-CODIS markers only
Correct answer: Compare the partial profile and note the reduced statistical weight
Partial profiles can be compared, but the statistical weight is reduced and limitations must be clearly communicated in the report.
Question 2: Which phenomenon occurs when a smaller DNA allele is preferentially amplified over a larger allele during PCR, leading to apparent homozygosity?
- Stutter
- Allelic dropout (Correct answer)
- Pull-up artifact
- Off-ladder allele
Correct answer: Allelic dropout
Allelic dropout occurs when one allele in a heterozygous sample fails to amplify, often due to low template DNA or degradation.
Question 3: In forensic DNA analysis, what does the term 'mixture ratio' refer to?
- The ratio of male to female contributors
- The relative proportion of DNA contributed by each individual in a mixed sample (Correct answer)
- The ratio of nuclear DNA to mitochondrial DNA
- The percentage of loci that show mixed profiles
Correct answer: The relative proportion of DNA contributed by each individual in a mixed sample
Mixture ratio describes the proportional contribution of each individual's DNA in a mixed sample, important for deconvolution.
Question 4: A forensic examiner observes a peak in a capillary electropherogram that is exactly one repeat unit smaller than a true allele. This artifact is called:
- Pull-up
- Stutter (Correct answer)
- Bleed-through
- Spike
Correct answer: Stutter
Stutter artifacts are minor peaks one repeat unit smaller (or occasionally larger) than the true allele, caused by strand slippage during PCR.
Question 5: When conducting Y-STR analysis on a sexual assault evidence sample, what is a key limitation forensic examiners must acknowledge?
- Y-STRs cannot be compared to a reference sample
- Y-STRs cannot distinguish between male relatives sharing the same patriline (Correct answer)
- Y-STR analysis is not admissible in US courts
- Y-STRs are only useful for maternal lineage analysis
Correct answer: Y-STRs cannot distinguish between male relatives sharing the same patriline
Y-STRs are identical among all paternally related males, so a match cannot exclude a brother, father, or other male paternal relatives.
Question 6: What statistical measure is used to express the probability that two unrelated individuals share the same DNA profile in a given population?
- Likelihood ratio
- Random match probability (Correct answer)
- Posterior probability
- Combined probability of inclusion
Correct answer: Random match probability
Random match probability (RMP) estimates the chance that a randomly selected unrelated person in the population would have the same DNA profile.
Question 7: A forensic analyst identifies three contributors in a DNA mixture. Which analytical approach is specifically designed for complex mixture interpretation?
- Simple allele counting
- Probabilistic genotyping software (Correct answer)
- Binary inclusion/exclusion
- Hardy-Weinberg manual calculation
Correct answer: Probabilistic genotyping software
Probabilistic genotyping software uses statistical models to evaluate contributor genotype combinations and compute likelihood ratios for complex mixtures.
CFC DNA Analysis & Interpretation 2
A forensic analyst obtains a DNA profile from a degraded sample with only 8 of 20 CODIS loci amplified.
What is the most appropriate course of action?