FDC DNA Analysis Techniques 3 — Questions and Answers
Question 1: What is the purpose of an internal size standard (ISS) in capillary electrophoresis?
- To normalize peak heights between samples
- To accurately size DNA fragments by providing reference peaks of known length (Correct answer)
- To separate alleles by charge rather than size
- To detect contamination in the sample
Correct answer: To accurately size DNA fragments by providing reference peaks of known length
The internal size standard provides reference peaks of known fragment sizes, allowing the instrument software to accurately determine the size of unknown allele peaks.
Question 2: Which of the following best describes Y-STR analysis?
- It analyzes maternal lineage through mitochondrial markers
- It analyzes paternal lineage using markers on the Y chromosome (Correct answer)
- It distinguishes male from female contributors in a mixture
- It detects mutations in autosomal microsatellites
Correct answer: It analyzes paternal lineage using markers on the Y chromosome
Y-STR analysis examines short tandem repeats on the Y chromosome, which is paternally inherited, allowing investigators to trace male lineage.
Question 3: What is the significance of Hardy-Weinberg equilibrium in forensic DNA statistics?
- It confirms that no mutations have occurred at an STR locus
- It allows genotype frequencies to be calculated from allele frequencies assuming random mating (Correct answer)
- It ensures that all contributors to a mixture are unrelated
- It validates the accuracy of the electropherogram
Correct answer: It allows genotype frequencies to be calculated from allele frequencies assuming random mating
Hardy-Weinberg equilibrium allows forensic analysts to calculate expected genotype frequencies by multiplying allele frequencies, assuming a randomly mating population.
Question 4: Which step in DNA extraction is responsible for breaking open cell walls and membranes to release DNA?
- Purification
- Quantification
- Lysis (Correct answer)
- Amplification
Correct answer: Lysis
The lysis step uses detergents, enzymes (such as proteinase K), or physical methods to break open cells and release DNA from the cellular matrix.
Question 5: In forensic DNA analysis, what is a 'mixture interpretation threshold' (analytical threshold)?
- The maximum number of contributors allowed in a mixture
- The minimum peak height below which data is not used for interpretation (Correct answer)
- The ratio of major to minor contributor in a mixture
- The number of loci required for a full profile
Correct answer: The minimum peak height below which data is not used for interpretation
The analytical threshold is the minimum peak height (in RFU) below which data is considered noise and excluded from interpretation to prevent false allele calls.
Question 6: Which type of DNA is most useful when biological evidence contains only hair shafts without follicular tissue?
- Nuclear DNA
- Mitochondrial DNA (Correct answer)
- Y-chromosomal DNA
- Autosomal DNA
Correct answer: Mitochondrial DNA
Hair shafts lack nuclei but contain abundant mitochondria, making mitochondrial DNA the method of choice when only the hair shaft (not root) is available.
Question 7: What does the product rule allow forensic analysts to calculate?
- The probability of a degraded DNA profile
- The combined profile frequency by multiplying genotype frequencies across multiple loci (Correct answer)
- The number of contributors in a mixed sample
- The likelihood that two samples share the same mitotype
Correct answer: The combined profile frequency by multiplying genotype frequencies across multiple loci
The product rule allows analysts to calculate a combined profile frequency by multiplying the individual genotype frequencies at each independently segregating locus.
FDC DNA Analysis Techniques 3
What is the purpose of an internal size standard (ISS) in capillary electrophoresis?