CSI Biological and Trace Evidence 3 — Questions and Answers
Question 1: Which of the following best describes the 'touch DNA' technique in forensic biology?
- DNA extracted from sweat left by skin contact with an object (Correct answer)
- DNA recovered from dried blood via touch transfer
- DNA obtained from insect larvae feeding on a body
- DNA amplified from a single hair shaft without a root
Correct answer: DNA extracted from sweat left by skin contact with an object
Touch DNA refers to epithelial cells shed from skin contact with surfaces, which can yield a low-template nuclear DNA profile.
Question 2: A criminalist finds a fiber with a trilobal cross-section and a distinctive dye absorption spectrum. This cross-section is most associated with which common fiber type?
- Cotton
- Wool
- Nylon 6,6 (Correct answer)
- Dacron polyester
Correct answer: Nylon 6,6
Nylon 6,6 fibers are commonly manufactured with a trilobal cross-section to improve texture and luster.
Question 3: When documenting a pooled bloodstain, what measurement is recorded to help reconstruct the event?
- The pH of the blood
- The area, shape, and perimeter characteristics of the pool (Correct answer)
- The coagulation time of the sample
- The blood type directly from the stain shape
Correct answer: The area, shape, and perimeter characteristics of the pool
Area, shape, and perimeter features of a pooled bloodstain document the extent and behavior of the deposit for reconstruction purposes.
Question 4: Which type of evidence packaging is most appropriate for moist biological samples to prevent mold and DNA degradation?
- Sealed plastic bag with a desiccant packet
- Paper bag or envelope after air drying the sample (Correct answer)
- Vacuum-sealed plastic pouch
- Plastic container with airtight lid
Correct answer: Paper bag or envelope after air drying the sample
Biological evidence should be air-dried before packaging in paper, which allows moisture to escape and prevents microbial degradation of DNA.
Question 5: In entomological evidence, the succession of insect species on a body can help estimate the postmortem interval (PMI). Which insect family is typically FIRST to colonize remains?
- Dermestidae (hide beetles)
- Calliphoridae (blow flies) (Correct answer)
- Silphidae (carrion beetles)
- Phoridae (humpbacked flies)
Correct answer: Calliphoridae (blow flies)
Blow flies (Calliphoridae) are usually the first colonizers of remains, arriving within minutes to hours of death to deposit eggs.
Question 6: What is the purpose of a substrate control when collecting a biological stain from a surface?
- To provide a positive reaction standard for the presumptive test
- To collect background material from an unstained area for comparison (Correct answer)
- To document the color of the surface under UV light
- To measure the pH of the stain for age estimation
Correct answer: To collect background material from an unstained area for comparison
A substrate control is collected from an adjacent unstained area to identify any background chemicals or DNA that could interfere with analysis.
Question 7: Glass refractive index (RI) is measured in forensic comparisons. Which instrument is the gold standard for measuring glass RI?
- Scanning electron microscope (SEM)
- GRIM3 (Glass Refractive Index Measurement) system (Correct answer)
- X-ray fluorescence spectrometer
- Fourier-transform infrared spectrometer (FTIR)
Correct answer: GRIM3 (Glass Refractive Index Measurement) system
The GRIM3 system uses the phase contrast/Becke line method to precisely measure glass refractive index for forensic comparisons.
CSI Biological and Trace Evidence 3
Which of the following best describes the 'touch DNA' technique in forensic biology?