ETC ETC Biological & DNA Evidence 1 — Questions and Answers
Question 1: Which presumptive test is used to detect the presence of seminal fluid at a crime scene?
- Acid phosphatase test (Correct answer)
- Luminol test
- Kastle-Meyer test
- Benzidine test
Correct answer: Acid phosphatase test
The acid phosphatase test detects the enzyme acid phosphatase found in high concentrations in seminal fluid; a positive result turns the reagent purple.
Question 2: What is the proper technique for collecting a dried bloodstain from a non-porous surface?
- Moisten a sterile swab with distilled water, collect the stain, air dry the swab completely, and package in paper (Correct answer)
- Scrape the stain into a plastic vial and seal immediately
- Use adhesive tape to lift the stain and place on a backing card
- Apply luminol to rehydrate and collect with a cloth swab sealed in plastic
Correct answer: Moisten a sterile swab with distilled water, collect the stain, air dry the swab completely, and package in paper
Dried bloodstains on non-porous surfaces should be collected with a moistened sterile swab, air-dried to prevent bacterial degradation, and packaged in breathable paper.
Question 3: What is touch DNA and from what type of evidence can it be collected?
- DNA from skin cells deposited through touch — collectible from surfaces like doorknobs, weapons, and steering wheels (Correct answer)
- DNA collected only from blood and saliva samples
- A laboratory amplification technique for degraded DNA samples
- DNA taken from decomposed remains only
Correct answer: DNA from skin cells deposited through touch — collectible from surfaces like doorknobs, weapons, and steering wheels
Touch DNA refers to trace skin cells (epithelial cells) left when a person touches a surface; it can be collected from any object a suspect may have handled.
Question 4: Why should biological evidence never be packaged in sealed plastic bags for long-term storage?
- Moisture trapped inside promotes bacterial growth and mold that degrades DNA (Correct answer)
- Plastic generates static electricity that damages DNA
- Plastic bags are not tamper-evident enough for evidence storage
- UV light penetrates plastic and degrades the sample
Correct answer: Moisture trapped inside promotes bacterial growth and mold that degrades DNA
Sealed plastic traps moisture, creating an environment where bacteria and mold thrive, rapidly degrading biological evidence and the DNA within it.
Question 5: Which body fluid is identified by the presence of p30 (PSA) protein confirmed by immunological testing?
- Seminal fluid (Correct answer)
- Blood
- Saliva
- Urine
Correct answer: Seminal fluid
p30, also known as prostate-specific antigen (PSA), is a protein found in semen and is used as a confirmatory marker for seminal fluid in sexual assault evidence.
Question 6: How should evidence technicians handle sexual assault evidence kits (SAFE kits) after collection?
- Refrigerate them at 2–8°C and submit promptly to the laboratory maintaining chain of custody (Correct answer)
- Store at room temperature in a locked cabinet until court date
- Freeze immediately at -20°C to preserve samples indefinitely
- Leave at room temperature for no more than 24 hours before disposal if not needed
Correct answer: Refrigerate them at 2–8°C and submit promptly to the laboratory maintaining chain of custody
SAFE kits must be refrigerated at 2–8°C to slow biological degradation and submitted promptly to the lab under documented chain of custody to preserve evidentiary integrity.
ETC ETC Biological & DNA Evidence 1
Which presumptive test is used to detect the presence of seminal fluid at a crime scene?