CGL Sample Preparation and Handling 3 — Questions and Answers
Question 1: A genealogical researcher wants to extract DNA from a century-old postage stamp for a historical project. Which part of the stamp is the primary DNA source?
- The ink layer on the front
- The adhesive (gum) on the back (Correct answer)
- The paper fiber matrix
- The perforated edges
Correct answer: The adhesive (gum) on the back
The adhesive on the back of an envelope or stamp can contain epithelial cells from the person who licked it, making it the primary DNA source.
Question 2: When mailing a DNA kit internationally for genealogical testing, which declaration is typically required on customs forms?
- Biological specimen — exempt from duty
- Human DNA — restricted biological material
- Non-infectious biological substance (UN3373) (Correct answer)
- Medical diagnostic sample — priority handling
Correct answer: Non-infectious biological substance (UN3373)
Non-infectious human biological samples for genealogical testing are classified as UN3373 (Biological Substance, Category B) for international shipping.
Question 3: Why should a genealogical DNA sample never be collected from a donor who has recently had a blood transfusion?
- The transfused blood contains viral markers that interfere with SNP arrays
- Transfused donor blood cells can skew autosomal results toward another individual (Correct answer)
- Blood transfusions render buccal cells inactive for 30 days
- The sample will be rejected by all major testing companies automatically
Correct answer: Transfused donor blood cells can skew autosomal results toward another individual
Blood transfusions introduce the donor's DNA into the recipient's bloodstream, which can contaminate a buccal sample and produce mixed or inaccurate results.
Question 4: Which preservation method is recommended for a fragile, water-damaged genealogical document before handling for research?
- Freeze-drying (lyophilization) followed by controlled humidity storage (Correct answer)
- Immediate photocopying to create a working copy
- Submerging in distilled water to stabilize the fibers
- Pressing between glass plates to flatten and dry
Correct answer: Freeze-drying (lyophilization) followed by controlled humidity storage
Freeze-drying removes moisture while preserving structure, and subsequent controlled-humidity storage prevents further deterioration of water-damaged documents.
Question 5: In the context of genealogical sample handling, what is the purpose of including a 'blank control' during DNA extraction?
- To calibrate the extraction equipment to the sample type
- To detect laboratory contamination introduced during the extraction process (Correct answer)
- To measure the baseline DNA concentration of the reagents
- To provide a reference sample for haplogroup comparison
Correct answer: To detect laboratory contamination introduced during the extraction process
A blank control (containing no sample DNA) run alongside extractions reveals whether any contamination was introduced by the lab environment or reagents.
Question 6: A genealogist is handling a daguerreotype for scanning. Which handling practice is most critical?
- Hold it firmly by the image surface to avoid dropping it
- Handle only by the edges or with cotton gloves to prevent surface fingerprints (Correct answer)
- Clean the surface with a damp cloth before scanning
- Store face-down after handling to protect the image
Correct answer: Handle only by the edges or with cotton gloves to prevent surface fingerprints
Daguerreotype image surfaces are extremely fragile and irreversibly damaged by fingerprints; handling by edges or with cotton gloves is essential.
Question 7: When preparing a DNA sample for Y-chromosome (Y-DNA) testing specifically, which male relative's sample is a valid substitute if the direct male-line subject is unavailable?
- A maternal uncle (mother's brother)
- A patrilineal male cousin (father's father's brother's son) (Correct answer)
- A maternal grandfather
- A half-brother through the mother
Correct answer: A patrilineal male cousin (father's father's brother's son)
Y-DNA is passed unchanged from father to son through the patrilineal line, so any male who shares the same unbroken patrilineal descent will carry the same Y-DNA.
CGL Sample Preparation and Handling 3
A genealogical researcher wants to extract DNA from a century-old postage stamp for a historical project.
Which part of the stamp is the primary DNA source?