CSI Biological and Trace Evidence 2 — Questions and Answers
Question 1: Which presumptive test for blood produces a blue-green color change in the presence of hemoglobin?
- Kastle-Meyer test
- Luminol test
- Leuco malachite green test (Correct answer)
- TMB test
Correct answer: Leuco malachite green test
Leuco malachite green (LMG) produces a blue-green color when it reacts with the peroxidase activity of hemoglobin.
Question 2: What is the primary reason investigators use an alternate light source (ALS) when searching for biological fluids?
- To sterilize the evidence surface
- To cause biological fluids to fluoresce or absorb light differently (Correct answer)
- To enhance fingerprint ridge detail
- To determine the age of bloodstains
Correct answer: To cause biological fluids to fluoresce or absorb light differently
ALS causes many biological fluids like semen and saliva to fluoresce, making them visible in low-contrast environments.
Question 3: A fiber recovered from a victim's clothing is identified as nylon. Which microscopic characteristic best distinguishes nylon from polyester fibers?
- Trilobal cross-section
- Circular cross-section with no striations
- Birefringence pattern under polarized light (Correct answer)
- Surface scales similar to hair cuticle
Correct answer: Birefringence pattern under polarized light
Polarized light microscopy reveals distinct birefringence patterns that differ between nylon and polyester, aiding fiber discrimination.
Question 4: When collecting soil evidence, what is the recommended minimum number of reference samples that should be taken from around a scene?
- One composite sample
- At least four perimeter samples plus a control (Correct answer)
- Two samples from opposite ends
- One sample adjacent to the evidence
Correct answer: At least four perimeter samples plus a control
At least four perimeter reference samples plus a control help establish the natural soil variation around the scene for comparison.
Question 5: Which enzyme is most commonly targeted in confirmatory tests for amylase to identify saliva?
- Lactate dehydrogenase
- Alpha-amylase (Correct answer)
- Acid phosphatase
- Prostate-specific antigen
Correct answer: Alpha-amylase
Alpha-amylase is produced in high concentrations in saliva and is the enzyme targeted in saliva identification assays.
Question 6: A hair root pulled out forcefully with an intact follicular tag is most useful for which type of analysis?
- Mitochondrial DNA analysis
- Nuclear DNA analysis (Correct answer)
- Microspectrophotometry
- Trace element profiling
Correct answer: Nuclear DNA analysis
A follicular tag contains nucleated cells, providing nuclear DNA suitable for STR profiling.
Question 7: What characteristic of glass fractures helps determine the direction from which a force was applied?
- The color of the glass fragments
- Radial and concentric crack patterns with hackle marks on edges (Correct answer)
- The weight of individual glass fragments
- The refractive index of the glass
Correct answer: Radial and concentric crack patterns with hackle marks on edges
Radial cracks form first and hackle marks on their edges point back toward the origin, revealing the direction of applied force.
CSI Biological and Trace Evidence 2
Which presumptive test for blood produces a blue-green color change in the presence of hemoglobin?