Forensic DNA & Evidence Profiling Glossary

This set covers the vocabulary, technical methods, and evidence-handling protocols required for forensic DNA profiling and the maintenance of evidence integrity as presented in the unit notes.

Forensic DNA Analysis

The process of identifying and evaluating biological evidence in criminal matters using DNA technologies, including collection, preservation, and chain of custody.

Locus (plural: loci)

The specific physical location of a gene — or of a variable region — on a chromosome.

Autosomal DNA

DNA found in chromosomes that are not sex chromosomes. Except for identical twins, no two people have the same autosomal DNA.

Short Tandem Repeat (STR)

Multiple copies of a short, identical DNA sequence (generally $5$ to $16$ repeats) arranged in direct succession in non-coding regions of chromosomes.

DNA Profiling

The process of determining the relative positions of DNA sequences at several specific locations; in forensic contexts, it evaluates specific STR locations.

Low Copy Number Analysis

The analysis of samples containing a very small amount of DNA, typically approximately $30$ cells or fewer.

Combined DNA Index System (CODIS)

The FBI’s program of support for criminal-justice DNA databases and the software used to run them (LDIS, SDIS, and NDIS).

National DNA Index System (NDIS)

An FBI-administered system authorized by the DNA Identification Act of $1994$ that allows comparison of crime-scene DNA profiles against convicted offenders and other crime-scene profiles.

Partial DNA Profile

DNA evidence that does not yield identifiable results at all $13$ core loci, often due to tiny or degraded samples.

RFLP (Restriction Fragment Length Polymorphism)

The earliest DNA fingerprinting method which used restriction enzymes (molecular scissors) to cut DNA at specific recognition sequences.

VNTR (Variable Number Tandem Repeats)

The predecessor to STR that used larger repeat units ($10\text{--}100$ base pairs) and required significantly more DNA.

DNA Fingerprinting

An early technique analyzing the lengths of DNA fragments (VNTRs) to show that no two people except identical twins have the same assortment of lengths.

Y-STR (Y-Marker Analysis)

An analysis targeting markers on the Y chromosome to isolate male DNA from a mixed sample or identify paternal lineage.

Amelogenin Gene

A sex-determination test used to distinguish female ($X,X$) from male ($X,Y$) sources, often on decomposed or skeletal remains.

SNP Analysis

A method examining single base changes rather than repeat counts; effective on highly degraded samples because it only requires a tiny intact amount.

Mitochondrial DNA (mtDNA)

Maternally inherited DNA found in high quantities within cells; it establishes maternal relatedness across generations rather than identifying a specific individual.

Chain of Custody

The unbroken, documented paper trail proving a piece of evidence is exactly what was collected, has never been tampered with, and can be tied to every individual who handled it.

Reference Samples

Material from a verifiable, documented source (such as a known victim or suspect) used for comparison with evidence of unknown origin.

Quality Assurance Standards (QAS)

Guidelines developed by SWGDAM and published by the FBI to ensure the quality and integrity of data a laboratory generates and uploads to CODIS.

Epithelial cells

Cells that cover the inner and outer linings of body cavities; they shed constantly and are a common source of DNA contamination from skin, saliva, or breath.

Cross-Contamination

A failure involving victim and suspect samples touching or the use of an uncleaned tool, which can manufacture a false association between people.

Liquid Sample Storage Requirement

Storage at approximately $4^{\nu}\text{C}$ in a controlled refrigerator with digital monitoring to slow biological breakdown.

Dried Biological Evidence Storage Requirement

Storage at room temperature ($20\text{--}24^{\nu}\text{C}$) in breathable brown paper bags to prevent moisture trapping and humidity-driven degradation.

Presumptive Testing

A preliminary step in the laboratory workflow to confirm a stain is biological (e.g., blood or semen) before committing limited resources to full DNA analysis.