FDC DNA Analysis Techniques 2 — Questions and Answers
Question 1: Which enzyme is used in PCR to synthesize new DNA strands during the extension step?
- RNA polymerase
- Taq polymerase (Correct answer)
- Ligase
- Helicase
Correct answer: Taq polymerase
Taq polymerase, derived from Thermus aquaticus, is thermostable and synthesizes new DNA strands during the extension step of PCR.
Question 2: In capillary electrophoresis, what is the role of the polymer matrix inside the capillary?
- To denature DNA fragments
- To separate DNA fragments by size (Correct answer)
- To amplify DNA fragments
- To label DNA fragments with fluorescent dyes
Correct answer: To separate DNA fragments by size
The polymer matrix in capillary electrophoresis acts as a molecular sieve, separating DNA fragments by size as they migrate through under an electric field.
Question 3: What does the term 'stutter' refer to in STR analysis?
- A primer that fails to anneal
- An artifact peak typically one repeat unit smaller than the true allele (Correct answer)
- A mixed profile from two contributors
- An off-ladder allele designation
Correct answer: An artifact peak typically one repeat unit smaller than the true allele
Stutter is a PCR artifact that produces a minor peak typically one repeat unit smaller than the true allele, caused by slippage during replication.
Question 4: Which technique is used to determine the sequence of nucleotides in a mitochondrial DNA hypervariable region?
- Fragment analysis
- RFLP
- Sanger sequencing (Correct answer)
- Southern blotting
Correct answer: Sanger sequencing
Sanger sequencing (chain termination sequencing) is the standard method used to determine the nucleotide sequence of mitochondrial DNA hypervariable regions.
Question 5: What is the primary advantage of using fluorescently labeled primers in STR analysis?
- They increase PCR amplification efficiency
- They allow simultaneous detection of multiple loci in a single capillary run (Correct answer)
- They prevent stutter artifact formation
- They eliminate the need for an internal size standard
Correct answer: They allow simultaneous detection of multiple loci in a single capillary run
Fluorescently labeled primers allow multiplexing, enabling simultaneous detection of multiple STR loci in a single capillary electrophoresis run using different dye colors.
Question 6: Which statistical measure is used to express the rarity of a DNA profile in the population?
- LOD score
- Random match probability (Correct answer)
- Bayes factor
- Hardy-Weinberg statistic
Correct answer: Random match probability
The random match probability (RMP) expresses the frequency of a DNA profile in a reference population, indicating how rare or common the profile is.
Question 7: In the context of forensic DNA analysis, what is a 'locus' dropout?
- When two alleles at one locus are indistinguishable
- When all alleles at a locus fail to amplify and produce no detectable signal (Correct answer)
- When a stutter peak exceeds 15% of the parent peak
- When an allele migrates outside the expected bin range
Correct answer: When all alleles at a locus fail to amplify and produce no detectable signal
Locus dropout occurs when both alleles at a locus fail to amplify, resulting in no detectable signal for that locus, often due to degraded or low-template DNA.
FDC DNA Analysis Techniques 2
Which enzyme is used in PCR to synthesize new DNA strands during the extension step?