BSFS Forensic Biology and DNA Analysis 1 — Questions and Answers
Question 1: Which technique is considered the gold standard for forensic DNA profiling in the United States today?
- Short tandem repeat (STR) analysis (Correct answer)
- Restriction fragment length polymorphism (RFLP)
- Mitochondrial DNA sequencing
- Y-chromosome typing only
Correct answer: Short tandem repeat (STR) analysis
STR analysis is the FBI's current standard because it is highly discriminating, requires only a small amount of DNA, and is fully automated for CODIS database searching.
Question 2: CODIS, the national DNA database used by forensic labs in the U.S., stands for:
- Combined DNA Index System (Correct answer)
- Criminal Offender DNA Identification System
- Centralized DNA Observation and Indexing System
- Comprehensive Offender Database and Identification System
Correct answer: Combined DNA Index System
CODIS is the FBI's national database that links DNA profiles from crime scenes with known offenders to assist in solving crimes across jurisdictions.
Question 3: The presumptive test for semen that detects the enzyme acid phosphatase is known as:
- AP spot test (acid phosphatase test) (Correct answer)
- PSA ELISA test
- Brentamine Fast Blue test
- Luminol test
Correct answer: AP spot test (acid phosphatase test)
The acid phosphatase spot test detects high concentrations of AP secreted by the prostate gland in semen, producing a purple color as a presumptive result.
Question 4: Polymerase chain reaction (PCR) is used in forensic DNA analysis primarily because it:
- Amplifies small or degraded DNA samples into quantities sufficient for analysis (Correct answer)
- Directly identifies the sequence of nucleotides without amplification
- Stains DNA bands for gel electrophoresis
- Creates a physical cast of chromosomal structure
Correct answer: Amplifies small or degraded DNA samples into quantities sufficient for analysis
PCR exponentially replicates target DNA sequences, enabling analysis of trace or degraded biological evidence that would otherwise be insufficient for profiling.
Question 5: Mitochondrial DNA (mtDNA) analysis is preferred over nuclear STR typing when:
- Evidence such as hair shafts without roots or aged bones contains insufficient nuclear DNA (Correct answer)
- A rapid result is needed in under an hour
- The suspect is male and Y-STR typing is not available
- The sample contains a mixture of two contributors
Correct answer: Evidence such as hair shafts without roots or aged bones contains insufficient nuclear DNA
mtDNA is present in thousands of copies per cell compared to two copies of nuclear DNA, making it recoverable from degraded evidence with minimal nuclear DNA.
Question 6: The ABO blood typing system classifies blood based on the presence of:
- Specific antigens on the surface of red blood cells (Correct answer)
- Antibody levels in plasma only
- The shape of red blood cells
- The concentration of hemoglobin in the sample
Correct answer: Specific antigens on the surface of red blood cells
ABO blood type is determined by the presence (or absence) of A and B antigens on red blood cell surfaces, which also determines corresponding plasma antibodies.
BSFS Forensic Biology and DNA Analysis 1
Which technique is considered the gold standard for forensic DNA profiling in the United States today?