Touch DNA
Definition
Minute quantities of epithelial cells transferred by skin contact with a surface, without leaving a visible stain. Collected by swabbing contact points such as door handles, weapon grips, or steering wheels. Highly susceptible to contamination and secondary transfer, which makes collection technique critical.
- DNA source
- Shed corneocytes (outer skin cells) from handling or contact
- Typical yield
- 1-500 picograms per sample
- Key limitation
- Susceptible to secondary and tertiary transfer from indirect contact
Common questions
What exactly is touch DNA and where does it come from?+
Touch DNA is nuclear DNA recovered from shed corneocytes, the outer skin cells that we naturally leave on surfaces when we handle objects or touch things. It comes from normal contact and handling, without any visible biological material like blood or saliva.
Why is touch DNA tricky to work with in investigations?+
It's highly prone to secondary and tertiary transfer, meaning DNA can get on a surface from indirect contact or contamination, not just from the person who actually handled the item. This makes it a central challenge to figure out who actually deposited the material. Shedding rates also vary dramatically between individuals and even at different times for the same person.
How much DNA can you get from a touch DNA sample?+
Touch DNA samples typically yield 1 to 500 picograms per sample, a relatively small amount. This makes the technique sensitive but also requires careful handling to avoid degradation or contamination.
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...
- Mitochondrial DNA (mtDNA)
- DNA located in mitochondria rather than the cell nucleus. Present in hundreds to thousands of copies per cell, making it recoverable from...
- Secondary Transfer
- The movement of a glass fragment from a primary surface (which contacted the broken glass) to a secondary surface (which contacted the...
- Substrate Control
- A sample of the unstained surface material from an area adjacent to a body fluid stain, collected alongside the stain and processed...
- ABO Blood Group System
- Classification of red blood cells by the presence or absence of A and B antigens on the cell membrane, determined by alleles...
- Allele Drop-in
- Appearance of a low-level allele in a PCR product from stochastic amplification of a contaminant molecule. More common in low-template reactions where...
- Allele Drop-Out
- Failure of one allele at a heterozygous locus to amplify in a low-template PCR reaction, producing an apparent homozygote. Increases dramatically below...
- Alternate Light Source (ALS)
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- Azoospermia
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- Biological Evidence
- Any material of biological origin recovered in a forensic context that can yield information relevant to an investigation. Includes blood, semen, saliva,...
- Corneocyte
- A terminally differentiated, anucleate cell forming the outermost skin layer (stratum corneum). Corneocytes shed continuously. Nucleated cells from deeper epidermal layers are...
Explained in these topics
- Biological Evidence Collection ProtocolsMinute quantities of epithelial cells transferred by skin contact with a surface, without leaving a visible stain. Collected by swabbing contact points such as...
- The Core Lab Sciences: Biology, Chemistry, PhysicsDNA recovered from skin cells deposited through handling or contact, without visible biological material. Highly sensitive but prone to secondary and tertiary...
- History and Development of Forensic BiologySkin cells (keratinocytes) shed when a person handles an object. Touch DNA samples are typically very small, containing fewer than 100 cells, requiring low-cop...
- The Scope of Biological Evidence in Forensic ScienceDNA deposited by skin-cell (epithelial cell) transfer when a person touches a surface. Typically a very small quantity of DNA. Susceptible to secondary transfe...
- Semen, Saliva and Other Body Fluids as EvidenceCellular material deposited by skin contact onto a surface, primarily anucleate corneocytes from the stratum corneum mixed with occasional nucleated keratinocy...
- Touch DNA and Trace Biological MaterialDNA deposited on a surface through physical contact, primarily from corneocytes shed from the outermost skin layer. Typically low in template quantity and may...
- Touch DNA, Hair, Bone, Teeth and Challenging SubstratesNuclear DNA recovered from shed corneocytes (outer skin cells) deposited on a surface by handling. Typically yields 1-500 pg per sample; subject to secondary t...