Reference Sample
Definition
A biological sample collected from a known individual (victim, suspect, or elimination source) for comparison against scene stains. Typically a buccal swab or blood draw. Reference samples are handled under the same chain of custody requirements as scene evidence.
- Common types
- Buccal swabs or EDTA blood tubes (in clinical settings). Known-location soil or plant samples (in botanical cases).
- Purpose
- Establish a baseline profile to distinguish known DNA or plant material from unknown or suspect sources.
Common questions
What's a reference sample in forensic science?+
A reference sample is a biological or botanical sample collected from a known source, such as a crime scene or a person, used to compare against other samples. In sexual assault cases, a buccal swab or blood sample from a victim establishes their DNA profile so the lab can tell apart the victim's DNA from DNA found elsewhere on the body.
Why do labs need a reference sample from the patient?+
The patient's reference sample eliminates confusion in DNA analysis. Without it, an examiner cannot distinguish between the patient's own DNA and foreign DNA from a suspect or unknown source on body-surface swabs.
How is a reference sample collected in a sexual assault kit?+
Common collection methods are a buccal swab (inside the cheek) or an EDTA blood tube. These are standard ways to capture DNA that establishes the patient's baseline genetic profile.
Related terms
- Chain of Custody
- The documented chronological record of who collected, handled, transferred, and examined a piece of evidence. For digital evidence, chain of custody includes...
- Double-Swab Technique
- A collection method for dried biological stains in which a moistened swab rehydrates and lifts the stain from the surface, followed immediately...
- Acetolysis
- Erdtman's 1934 extraction method. The sample is treated with a 9:1 mixture of acetic anhydride and concentrated sulphuric acid, which dissolves cellulose...
- Alternate Light Source (ALS)
- A device emitting light at selected wavelengths (typically 415 to 535 nm) used to detect biological fluids that fluoresce or absorb light...
- Blank Control
- A sample known to contain none of the target material, processed in parallel with real exhibits to detect laboratory contamination. A positive...
- Kit Shelf Life
- The period during which an unused sealed SAFE kit remains usable, typically 2-5 years depending on the manufacturer and storage conditions. Expired...
- SAFE Kit
- Sexual Assault Forensic Evidence kit. The standardised collection of containers and instructions used to gather biological and trace evidence from a sexual...
- Substrate Control
- A sample of the unstained surface material from an area adjacent to a body fluid stain, collected alongside the stain and processed...
- Taphonomy
- The systematic modification of bone by environmental processes after death, operating over the burial or exposure interval. Includes weathering, soil staining, sun...
- Touch DNA
- Minute quantities of epithelial cells transferred by skin contact with a surface, without leaving a visible stain. Collected by swabbing contact points...
- Voucher Specimen
- A preserved specimen formally deposited in a collection or retained in the case file as a permanent reference. In forensic entomology, the...
- Wet Evidence Drying
- The mandatory air-drying step for any wet biological sample before sealing. Sealing wet evidence traps moisture, promotes bacterial growth, and degrades DNA....
Explained in these topics
- Biological Evidence Collection ProtocolsA biological sample collected from a known individual (victim, suspect, or elimination source) for comparison against scene stains. Typically a buccal swab or...
- Botanical Evidence Collection and PreservationA sample collected from a known location, typically the crime scene or a control site, used as a comparator against samples from suspects or unknown objects.
- The SAFE Kit: Components and Collection SequenceA biological specimen taken from the patient to establish their own DNA profile. A buccal swab or EDTA blood tube. Used by the laboratory to distinguish the pa...