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DNA Extraction and Quantitation for Forensic Analysts


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2p rule

The NRCII report recommends using this approach for dealing with homozygotes.



Automated Fingerprint Identification System

ABO blood typing

A commonly used genetic typing test that uses antibodies to detect variations on the surface of human red blood cells. Individuals are typed as having A, B, O, or AB type blood by testing liquid or stains from body fluids (e.g., blood, saliva, vaginal secretions). One out of every three randomly selected pairs of people have the same ABO blood type.


If prior adverse expert testimony has established certain facts or conclusions, the more of those facts and conclusions that the expert can use to bolster his opinions, the stronger those opinions will appear.

Actual innocence claim

Is equivalent to an assertion of at least a 51-percent chance that the defendant would not have been convicted if exculpatory test results had been obtained at the time of trial. In a case involving DNA evidence, a successful Actual Innocence claim entitles the defendant to DNA testing. The testing is funded by the state, not by the defendant.

Adenosine Triphosphate (ATP)

Main source of energy for biochemical reactions within the cell.

Admissible Evidence

Admissible evidence, in a court of law, is any testimonial, documentary, or tangible evidence that may be introduced to a factfinder — usually a judge or jury — in order to establish or to bolster a point put forth by a party to the proceeding. In order for evidence to be admissible, it must be relevant, without being prejudicial, and it must have some indicia of reliability.

Admitted evidence

If the expert's opinion is based on facts already admitted into evidence or that will be admitted, the power of the conclusions is greatly enhanced. The argument becomes a "building block philosophy": "If A, B and C are already established, then D must be true."


One who swears to an affidavit; broadly : deponent


A sworn voluntary declaration of facts, findings, conclusions or opinions of the declarant, given with their affirmation that the contents are true. Is voluntarily made without any cross-examination of the affiant and, therefore, is not the same as a deposition, a record of an examination of a witness or a party made either voluntarily or pursuant to a subpoena, as if the party were testifying in court under cross-examination. A pleading — a request to a court to exercise its judicial power in favor of a party that contains allegations or conclusions of facts that are not necessarily verified — differs from an affidavit, which states facts under oath.


A different form of a gene at a particular locus. The characteristics of a single copy of a specific gene, or of a single copy of a specific location on a chromosome. For example, one copy of a specific short tandem repeat (STR) region might have 10 repeats, while the other copy might have 11 repeats. These would represent two alleles of that STR region.

Allele Frequencies

Term used to characterize genetic variation of a species population.

Allelic dropout

Failure to detect an allele within a sample or failure to amplify an allele during PCR.

Allelic ladder

Comprised of DNA fragments that represent common alleles at a locus.

Alternate light source (ALS)

Equipment used to produce visible and invisible light at various wavelengths to enhance or visualize items of evidence (fluids, fingerprints, clothing fibers, etc.). The light will cause possible biological stains to change color or fluoresce, assisting in the location process.


Non-coding regions of DNA containing a restriction site for the enzyme Alu 1. The sequences are about 300 base pairs long and are repeated several thousand times throughout the genome.


A gene present on the X and Y sex chromosomes that is used in DNA identification testing to determine the gender of the donor of the DNA in a biological sample.

Amorphous medulla

An amorphous medulla has no distinct form, pattern, or shape when viewed with a transmitted light microscope


Amplified DNA fragments.


Producing multiple copies of a chosen DNA region, usually by PCR (Polymerase Chain Reaction).

Amplified Fragment Length Polymorphisms (AFLP or AmpFLP)

A highly sensitive method for detecting polymorphisms in DNA. DNA first undergoes restriction enzyme digestion, and a subset of DNA fragments is then selected for PCR amplification and visualization.


The anagen root is the active growth phase of a hair follicle in the hair growth cycle

Analytical Threshold

An acceptable "Relative Fluorescence Units" (RFU) level determined to be appropriate for use in the PCR/STR DNA typing process. A minimum threshold for data comparison is identified by the specific forensic laboratory doing the testing through independent validation studies.

Angular aperture

The angle (or cone) of light rays capable of entering the front lens of the objective from a point in the object. If the angular aperture of an objective is increased, more light rays from the specimen can be taken in by the lens, increasing the resolving power.

Annealing Temperature Ta

An annealing temperature is approximately 5°C below the lowest melting temperature Tm of the pair of primers used.


A positively charged electrode.

Appellate court

A court of appeals that hears appeals from lower court decisions.


 Any non-allelic product of the amplification process (Stutter or Minus A) or anomaly of the detection process (Pull-up or Spike).


American Society of Crime Lab Directors


A lawyer, counselor or advocate serving as a party's representative in the dispute-resolution process.

Attorney-client privilege

The client's right to refuse to disclose and to prevent any other person from disclosing confidential communications between the client and the attorney.

Attorney work-product rule

The rule providing for qualified immunity of an attorney's work product from discovery or other compelled disclosure.


Chromosomes which are not sex chromosomes.



Base Pairing

A,T,C and G are molecular building blocks of DNA that only continue in specific "base" pairs, e.g.,A only pairs with T, and C only pairs with G


Residual signal associated with an instrument's blank response.


The four building blocks of DNA are called bases. The building blocks are Cytosine, Guanine, Thymine, Adenine and are commonly referred to as C, G, T, A.

Bayesian probability

System of probability based on beliefs in which the measure of probability is continuously revised as available information changes.

Bench notes

A laboratory analyst's recorded notes.


Pertaining to both alleles, e.g. single nucleotide polymorphisms display two alternate forms and are biallelic.


A trial that is divided into two stages, such as for guilt and punishment or for liability and damages; also termed two-stage trial.

Bindle paper

Clean paper folded for the containment of trace evidence, sometimes included as part of the packaging for collecting trace evidence.

Biohazard bag

A container for materials that have been exposed to blood or other biological fluids and have the potential to be contaminated with hepatitis, AIDS, or other contagions.

Biological Evidence

Evidence commonly recovered from crime scenes in the form of hair, tissue, bones, teeth, blood or other bodily fluids.

Biological fluids

Fluids that have human or animal origin, most commonly encountered at crime scenes (e.g., blood, mucous, perspiration, saliva, semen, vaginal fluid, and urine).

Blind testing

In a blind test, analysts do not know they are being tested. In most forensic DNA laboratories, blind tests are not used. 

In practice, it is almost impossible to design and implement an effective blind PT (proficiency test) program in forensic science. Most attempts have failed because they could not produce an effective case scenario with realistic representation of the pre-laboratory steps. Others failed because the analyst recognized that the supposed "evidence" was a manufactured artifact. Overall, it has proven impossible to realize the theoretical extra benefits of blind testing, and resources have been devoted to promoting better quality external open tests.

Bloodborne Pathogens

Disease-causing microorganisms that are present in blood and can cause disease in humans. Pathogens include, but are not limited to, hepatitis B virus (HBV) and human immunodeficiency virus (HIV).


The perimeter or border surrounding potential physical evidence related to the crime.

Bovine serum albumin (BSA)

Protein fraction of serum isolated from the bovine family (i.e. cow, ox, buffalo).


Buckling is a disruption of the hair shaft demonstrating itself as an abrupt change in direction with or without a slight twist. This feature may be due to genetic factors, or it may result from damage (i.e., hair treatments).


Chemical solution that maintains a relatively constant pH even with the addition of strong acids or bases.

Business record

The expert's report may constitute a record of a regularly conducted activity.



Cambridge Reference Sequence (CRS)

A "master template" of the HVR-1 region of mitochondrial DNA.

Cambridge Reference Sequence, revised (rCRS)

The rCRS sequence is a modified version of the original Cambridge Reference Sequence (GenBank #J01415.0 gi:337188) of Anderson et al (1981).

Capillary Electrophoresis (CE)

The platform for CE uses narrow silica capillaries (or tubes) containing a polymer solution through which the negatively charged DNA molecules migrate under the influence of a high voltage electric field. Important advantages of the CE technique, compared to slab gel electrophoresis, include quicker and more easily automated analyses

Cartilage Hair Hypoplasis

A hair disorder that results in abnormally fine, sparse, and lightly colored hair that is usually short.

Case agent

Lead investigator who is permitted to remain in the courtroom throughout the trial, even though the investigator will also have a role as a testifying witness.

Case file

The collection of documents comprising information concerning a particular investigation. (This collection may be kept in case jackets, file folders, ring binders, boxes, file drawers, file cabinets, or rooms. Sub-files are often used within case files to segregate and group interviews, media coverage, laboratory requests and reports, evidence documentation, photographs, videotapes, audiotapes, and other documents.)

Case Identifier

The alphabetic and/or numeric characters assigned to identify a particular case.

Case theories

Every case going to court needs a theory which describes the case. The theory must include a statement of the facts, an explanation of what happened, the law that supports your advocacy, and the verdict you feel is deserved. Case theory should contain and clearly state the outcome that you believe to be fair and just. You should explain your cause, whether or not you are defending or acting, and offer up ways to prove your theory. Case theory is strongest if one major issue is focused on as opposed to a borage of facts that could be argued. Every argument and fact presented should support the first theory that you are trying to get across. The case theory should be supported by some sort of evidence.


The catagen phase is the transitional phase of the hair follicle from the active growth phase (anagen) to the resting growth phase (telogen) in the hair growth cycle.


A negatively charged electrode.


Positively charged ion. (e.g., K+, Na+, NH4+)


Caucasoid is an archaic anthropological term designating the peoples originating from Europe and the Indian subcontinent.


The smallest component of life capable of independent reproduction and from which DNA is isolated for forensic analysis.

Central Distribution (pigment)

The distribution and concentration of the pigment in the center of the cortex.

Chain of Custody

A record of individuals who have had physical possession of the evidence and the process used to maintain and document the chronological history of the evidence. (Documents can include, but are not limited to, name or initials of the individual collecting the evidence; each person or entity subsequently having physical possession of it; dates the items were collected or transferred; from where the item(s) were collected; agency and case number; victim's or suspect's name (if known); and a brief description of the item.)


Property of certain substances to disrupt the structure of water. Promotes the solubility of non-polar substances and the elution from or movement through a chromatographic medium of an otherwise tightly bound substance.


The release of light (photons) as the result of a chemical reaction.

Chi-squared Test of Association

Comparison of the observed frequencies with the frequencies that would be expected if the null hypothesis of no association were true.


A chemical used in organic extraction. When used with phenol, promotes a sharp interface between the organic and aqueous layers.


The biological structure by which hereditary information is physically transmitted from one generation to the next. Located in the cell nucleus, it consists of a tightly coiled thread of DNA with associated proteins and RNA. The genes are arranged in linear order along the DNA.


The process of removing biological and/or chemical contaminants from tools and/or equipment.

CODIS Combined DNA Index System

A collection of databases of DNA profiles obtained from evidence samples from unsolved crimes and from known individuals convicted of particular crimes. Contributions to this database are made through State crime laboratories and the data are maintained by the FBI. Learn more about CODIS on the FBI's Web site.

CODIS core loci

Thirteen STR (short tandem repeat) sequences that have been selected for the Combined DNA Index System (CODIS).

Cold hit

When CODIS recognizes a match between an offender and forensic profile, it is referred to as a "cold hit."


The process of identifying, documenting, gathering, and packaging or retaining physical evidence.

Compulsory Process

Method by which a person sought as a witness is forced to appear before the court. Compulsory process encompasses not only a subpoena, which is a command to appear at a particular time and location to provide testimony upon a certain matter, but also a bench warrant, a written order commanding a law enforcement officer to seize the person named and bring them into court. The Sixth Amendment to the U.S. Constitution provides that the accused in criminal prosecutions shall have the right "to have compulsory process for obtaining witnesses in his favor."

Confrontation clause

The Sixth Amendment provision generally guaranteeing a criminal defendant's right to confront an accusing witness face-to-face and to cross-examine that witness. Note: This right may be overridden if the witness is especially vulnerable, such as a child who is an alleged victim of sexual abuse. Even then, the defendant's attorney must have an opportunity to examine the witness while the defendant observes by means of closed-circuit television or similar protective means.

Combined Paternity Index (CPI)

Odds ratio that depicts the likelihood of the alleged father being the biological father, in comparison to the likelihood of a random unrelated man in the population being the biological father.

Comparison microscope

Two microscopes joined by an optical bridge to present a split-view, side-by-side comparison of two specimens; for example, two hairs on separate slides.


The combination of demonstrated knowledge, skills, and abilities.

Competency Test

A test given during training to assess the ability of a trainee.

Compulsory Process

. Method by which a person sought as a witness is forced to appear before the court. Compulsory process encompasses not only a subpoena, which is a command to appear at a particular time and location to provide testimony upon a certain matter, but also a bench warrant, a written order commanding a law enforcement officer to seize the person named and bring them into court. The Sixth Amendment to the U.S. Constitution provides that the accused in criminal prosecutions shall have the right "to have compulsory process for obtaining witnesses in his favor."


Lenses or mirrors which bow in.

Confidence Interval

Estimated range of values (calculated from a given set of sample data) that is likely to include an unknown population parameter.

Confirmatory Test

A simplistic method for estimating genotype frequency by direct counting of the number of times a genotype is observed in a database.

Confrontation Clause

The Confrontation Clause of the Sixth Amendment to the United States Constitution provides that "in all criminal prosecutions, the accused shall enjoy the right...to be confronted with the witnesses against him." Generally, the right is to have a face-to-face confrontation with witnesses who are offering testimonial evidence against the accused in the form of cross-examination during a trial. The Fourteenth Amendment makes the right to confrontation applicable to the states and not just the federal government. The right only applies to criminal prosecutions, not civil cases or other proceedings.


The undesirable transfer of material to physical evidence (DNA) from another source.

Contempt power

Every court has inherent power to punish a person for contempt of its judgments or decrees or for conduct within or near the court which is contemptuous.

Continuous (medulla)

A form of hair medullation where the visible medulla extends uninterrupted along a length of hair shaft.

Control Samples

Cuttings, swabbings, etc., from unstained adjacent material. A control sample is material of a known source that presumably was uncontaminated during the commission of the crime (e.g., a sample to be used in laboratory testing to ensure that the surface on which the sample is deposited does not interfere with testing. For example, when a bloodstain is collected from a carpet, a segment of unstained carpet must be collected). The control sample should be taken adjacent to the biological stain being collected.


Tests designed to demonstrate that a procedure worked correctly and performed in parallel with experimental samples.


Lenses or mirrors that bow out.


A convolution is an abrupt rotation of the hair shaft that can occur naturally, from disease, or as a result of mechanical force.


This involves a smooth blend of verbal testimony with charts, drawings, exhibits and other tangible items to exemplify the spoken word.


The cortex is the primary anatomical region of a hair between the cuticle region and the medullary region composed of elongated and fusiform cells.

Cortical Fusi

Cortical fusi are the small spaces within the hair shaft that appear as microscopic dark structures, commonly at the proximal end of hairs; they can be filled with air or liquid.


The phase of the dispute-resolution process in which the opposing counsel asks witnesses questions in order to test the truth, accuracy or thoroughness of direct testimony.

Cross Contamination

The undesirable transfer of material between two or more sources of physical evidence.

Cross Projection Sketch

Also commonly referred to as an Exploded View Sketch. This type of sketch views the scene from above similar to a Birds-eye View but with the walls folded down. This sketch is used to show evidence on the walls such as blood spatter and bullet holes.

Cross-sectional shape

The cross-sectional shape is the shape of a hair shaft cut and viewed at a right angle to its longitudinal axis.


A hair shaft form that is bent into or towards a spiral form.


A hair shaft form with slight curvature but does not exhibit waviness or does not curl back upon itself to form a circle.


The cuticle is the outermost region of a hair and is composed of layers of overlapping scales.

Cycle Threshold (CT)

Cycle number (in qPCR) at which the fluorescence generated within a reaction well exceeds the defined threshold. The threshold is arbitrarily defined by the manufacturer to reflect the point during the reaction at which a sufficient number of amplicons have accumulated.


The viscid, semifluid matter contained within the plasma membrane of a cell, excluding the nucleus.




  1. To attempt to use the same court expert's impartial fact testimony to create reasonable doubt with the jury about material DNA evidence and testing results in the case, perhaps due to claims of:
    • Contamination.
    • Breaks in the chain-of-custody.
    • Failure to comply with accepted lab standards and protocol, or other claims.
  2. Also, defense or defense attorney, the counsel representing the defendant in a lawsuit or criminal prosecution.

Degenerate Primer

A PCR primer sequence is called degenerate if some of its positions have several possible bases.


The fragmenting, or breakdown, of DNA by chemical or physical means.

Demonstrative materials/aids

Charts, graphs, drawings, computer graphics, models, audio and video presentations, or any other device used to demonstrate, characterize or explain verbal testimony.

Demonstrative evidence

Refers to an item that is not from the crime scene itself but that can illustrate (demonstrate) a concept. An example of demonstrative evidence is an anatomically correct model used to show where the victim was injured. Charts, graphs, drawings, computer graphics, models, audio and video presentations, or any other device used to demonstrate, characterize or explain verbal testimony.


Separation of the two strands of a DNA double helix.


The person being deposed.


The taking and recording of testimony of a witness under oath before a court reporter in a place away from the courtroom before trial. Includes:
  • A witness's out-of-court testimony that is reduced to writing (usually by a court reporter) for later use in court or for discovery purposes.
  • The session at which such testimony is recorded.
  • Sworn testimony given outside the presence of the trier of fact in the presence of a court reporter, counsel, and the parties to find out what the expert knows, what sort of witness the expert will be, and to lock the expert into a position.

Depth of field

Axial resolving power of an objective, which is measured parallel to the optical axis.

Depth of focus

The range of distances between a lens and image plane for which the image formed by the lens at a given setting is clearly focused. With a high numerical aperture microscope objective, the depth of field is very shallow, but the depth of focus can be quite deep and reach several millimeters.

Dermal papilla

Connective living tissue from which hair is generated from the follicle in the thick layer of the skin below the epidermis

Destructive testing

A process by which tangible items are disposed of during an examination.

Dideoxy sequencing

Dideoxynucleotide sequencing, also known as the "Sanger method," is a technique which uses dideoxyribose instead of deoxyribose to stop the synthesis of a complementary DNA strand at various points when sequencing.

Differential extraction

A procedure in which sperm cells are separated, or extracted, from all other cells in a sample.


The processes used before a trial to uncover the facts of the case.

Diffuse Light

light reflected uniformly in all directions regardless of what angle the light comes in at.

Direct examination

The procedure during a trial or hearing that first presents a witness's testimony to the trier of fact.

Discontinuous (medulla)

A form of hair medullation where the visible medulla is interrupted or fragmented along a length of hair shaft.

Discriminating Power

The ability of a blood grouping technique to differentiate between individuals selected at random. This can also be applied to other analytical techniques in forensic science.

Disposable instruments

Items that will be used only once to collect evidence, such as biological samples, then discarded to minimize contamination (e.g., tweezers, scalpel blades, droppers).


Not similar or alike; different in appearance, properties, or nature; unlike.

Distal End

The end of the hair away from the root; towards the tip.

Dithiothreitol (DTT)

Reducing or deprotecting agent for thiolated DNA. (1,4-Dicaptomercapto-2,3-butanediol; formula is C4H10O2S2)

DNA (Deoxyribonucleic acid)

Often referred to as the "blueprint of life," DNA is the genetic material present in the nucleus of cells which is inherited half from each biological parent. DNA is a chemical substance contained in cells, which determines each person's individual characteristics. An individual's DNA is unique except in cases of identical twins.

DNA Analysis

The process of testing to identify DNA patterns or types. In the forensic setting, this testing is used to exclude or include individuals as possible sources of body fluid stains (blood, saliva, semen) and other biological evidence (bones, teeth, hair). This testing can also be used to indicate parentage.

DNA fingerprinting

Analyses of the lengths of the fragments reveal that when looking at multiple VNTRs (variable number of tandem repeats) within and between individuals, no two people have the same assortment of lengths. This technique became known to the public as "DNA fingerprinting" because of its powerful ability to discriminate between unrelated individuals.

DNA mixtures

A sample that contains the DNA of more than one individual.

DNA Profile

The result of determining the relative positions of DNA sequences at several locations on the molecule. Each person (except identical twins) has a unique DNA profile when used in the context of the CODIS database, which evaluates 13 specific DNA locations.


Written notes, audio/videotapes, printed forms, sketches, and/or photographs that form a detailed record of the scene, evidence recovered, and actions taken during the search of the crime scene, including chain of custody information.

Double Helix

The shape the DNA assumes after it replicates during cell life.




The graphic representation of the separation of molecules by electrophoresis or other means of separation.


A method of separating large molecules (such as DNA fragments) from a mixture of similar molecules. An electric current is passed through a medium at a different rate, depending on its electrical charge and size. Separation of DNA markers is based on these differences.

Elimination/Reference samples

A term used to describe a sample of known source taken for comparison purposes.

Example-An elimination sample is one of known source taken from a person who had lawful access to the crime scene (e.g., blood or cheek [buccal] swabs for DNA analysis, fingerprints from occupants, tire tread impressions from police vehicles, footwear impressions from emergency medical personnel) to be used for comparison with evidence of the same type.

A reference sample is material of a verifiable/documented source which, when compared with evidence of an unknown source, shows whether an association or linkage exists between an offender, crime scene and/or victim (e.g., a carpet cutting taken from a location suspected as the point of transfer for comparison with the fibers recovered from the suspect's shoes, a sample of paint removed from a suspect's vehicle to be compared with paint found on a victim's vehicle following an accident, or a sample of the suspect's and/or victim's blood submitted for comparison with a bloodstained shirt recovered as evidence).


Property of a culture or subculture whose members are readily distinguishable based on traits originating from a common source (e.g. racial, national, linguistic, etc.). Members of an ethnic group are often presumed to be culturally or genetically similar; this is not necessarily true.


Something that can help identify the responsible persons, establish an element of crime, reconstruct crime events or link crimes.

Evidentiary samples

A generic term used to describe physical material/evidence discovered at crime scenes that may be compared with samples from persons, tools, and physical locations.


Two samples cannot have come from the same source.


A DNA test result indicating that an individual is excluded as the source of the DNA evidence. In a criminal case, "exclusion" does not necessarily equate to "innocence." This occurs when one or more types from a specific location in the DNA of a known individual are not present in the type(s) for that specific location in the DNA obtained from an evidence sample.

Exculpatory evidence

Any evidence that supports the defendant's claim of innocence or may show he is guilty of a lesser crime than that with which he is charged.

Exogenous DNA

DNA originating outside an organism that has been introduced into the organism.


An enzyme that cleaves nucleotides one at a time from an end of a polynucleotide chain. An enzyme that hydrolyzes phosphodiester bonds from either the 3' or 5' terminus of a polynucleotide molecules.

Ex parte Communication

A communication between counsel and the court when opposing counsel is not present.

Expected Heterozygosity

Mean value of all the expected values found for all loci in a sample.

Expert opinion

An opinion offered by an expert witness — a major exception to the general rule of evidence, which typically requires that testimony be based on personal knowledge. Because of their knowledge, training and experience, experts are allowed to render opinions about what happened rather than merely recite what their senses recorded.

Expert System

A software program or set of software programs designed to rapidly process data without human intervention.

Expert Testimony

Presentation of verbal or written evidence in the dispute-resolution process in a scientific, professional, technical or specialized field, usually beyond the knowledge of laymen.

Expert Witness

A person who, because of education, training or experience, has special knowledge not held by the general public.


A special skill or knowledge in a particular field.

External testing

An external test is one that is created and administered by an outside agency.



Fact finder

Court or administrative agency staff who determine, from the evidence of a case, the facts as presented by one party and denied/contested by the other. Whoever has the responsibility of rendering the verdict in a case. This is the jury in a jury trial or the judge in a bench trial.

First responder

The initial responding law enforcement officer and/or other public safety official or service provider arriving at the scene prior to the arrival of the investigators in charge.

Federal Rules of Evidence

Body of evidentiary rules, used in federal court and adopted in many state courts, which generally constitute a summary of the law of evidence in many jurisdictions. See Federal Rules of Evidence published by the Legal Information Institute, Cornell University Law School.

Focal plane

A plane that is perpendicular to the axis of a lens or mirror and passes through the focus.

Forensic Hit

A CODIS match between two or more crime scene profiles.

Forensic witness/expert

A person who testifies at a dispute-resolution trial or hearing on the basis of scientific, professional, technical or specialized knowledge, training or experience. A person who is allowed (by law) to give opinions in law-related settings rather than merely recite facts gained from the senses. Forensic opinions are sought to explain past, present and future events.

Forensic Index

DNA profiles developed from crime scene evidence and uploaded into CODIS are maintained in the forensic index of the database.

Forensic Science

The application of science to analyze evidence involved in criminal and civil litigation.

Forensic unknowns

DNA profiles obtained from crime scene evidence samples that are unmatched to a known individual.


The result of the differential extraction; separating sperm cells from all other DNA material.

Fragile evidence

Evidence that will lose its evidentiary value if not preserved and protected, either because of its nature or the conditions at the scene (e.g., blood in the rain).


Spindle-shaped; tapering from the middle towards each end. This shape is commonly seen in cortical cells and cortical fusi.




The basic unit of heredity; a functional sequence of DNA in a chromosome.

Genetic loci

Places in the genetic material of an organism where specific DNA sequences can be found.


The study of the patterns of inheritance of specific traits.


All the genetic material in the chromosomes of a particular organism; its size is generally given as its total number of base pairs.


The genetic constitution of an organism, as distinguished from its physical appearance (its phenotype). The designation of two alleles at a particular locus is a genotype.




One of the numerous fine and generally cylindrical filaments that grow from the skin or integument of animals, esp. of most mammals, of which they form the characteristic coat; applied also to similar-looking filamentous outgrowths from the body of insects and other invertebrates. These are usually of different structures.

Hair cuticular cast

A freely movable, firm yellowish-white material ensheathing scalp hairs resulting from scalp disorders such as psoriasis or seborrhoeic dermatitis.


A way of denoting the collective genotype of a number of closely linked loci on a chromosome.


A protein present in blood serum that combines with hemoglobin to form a complex that is rapidly removed from the circulation by the liver.

Hardy-Weinberg (Equilibrium)

In a large random intrabreeding population, not subjected to excessive selection or mutation, the gene and genotype frequencies will remain constant overt time. The sum of p²+2pq+q² applies at equilibrium for a single allele pair where p is the frequency of the allele A, q is the frequency of ap² is the frequency of genotype AA, q² is the frequency of aa, and 2pq is the frequency of Aa.


Any proceeding before a judge or other magistrate (such as a hearing officer or court commissioner) without a jury in which evidence and/or argument is presented to determine some issue of fact or both issues of fact and law. While technically a trial with a judge sitting without a jury fits the definition, a hearing usually refers to brief sessions involving a specific question at some time prior to the trial itself, or such specialized proceedings as administrative hearings. In criminal law, a "preliminary hearing" is held before a judge to determine whether the prosecutor has presented sufficient evidence that the accused has committed a crime to hold him/her for trial.


(1) Traditionally, testimony that is given by a witness who relates not what he or she knows personally but, rather, what others have said; this testimony is therefore dependent on the credibility of someone other than the witness. Such testimony is generally inadmissible under the Federal Rules of Evidence. (2) A statement of conduct made by a witness outside the presence of the trier of fact, with no opportunity for cross-examination by the opposition. There are certain exceptions to the hearsay exclusion that are based on indicators of reliability attending such declarations or conduct, and that make them admissible as evidence at trial.


The deep red, non-protein, ferrous component of hemoglobin. C34H32FeN4O4


The transmission of characteristics from one generation to the next.


The presence of more than one mtDNA type within a single individual.


The probability that a given loci will be heterozygous in a randomly selected individual; having two different alleles at one locus.


If two alleles are different at one locus, the person is heterozygous at that genetic location.


Health Insurance Portability and Accountability Act of 1996.


A type of basic protein that forms the unit around which DNA is coiled in the nucleosomes of eukaryotic chromosomes. Arginine- and lysine-rich basic proteins making up a substantial portion of eukaryotic nucleoprotein.

HLA DQ-alpha

A polymorphic gene in the Human Leukocyte Antigen (HLA) region of chromosome 6 that has been well studied and analyzed for many purposes including paternity testing, transplantation biology, and human DNA identification testing.


If two alleles at a locus that are indistinguishable, the person is homozygous at that genetic location.


An organic residue of decaying organic matter.


A bicyclic aromatic compound, which when added to phenol turns the aqueous phase orange, making it easier to differentiate in the organic extraction.


An area on the DNA which can have many different alleles in differing sequences.

Hypervariable Control Region

The D-loop of mitochondrial DNA in which base pairs of nucleotides repeat.




A general term for the kind of globular blood proteins that constitute antibodies. A tetrameric protein composed of two identical light chains and two identical heavy chains. Specific proteins produced by derivatives of B lymphocytes that interact with and help protect an organism from specific antigens.


An attack on a witness which questions credibility, believability, or opportunity for testing or observation.

in limine

Preliminary rulings by the court concerning proposed testing, experiments, demonstrations or models.


An accusatory document by which a grand jury brings criminal charges against an individual or entity, usually required for felonies and other crimes.


Two samples could have come from the same source.

Inclusion (Failure to Exclude)

The inability to exclude an individual as a possible source of a biological sample. This occurs when all types from a specific location in the DNA of a known individual are also present in the types for that specific location in the DNA obtained from an evidence sample.


A situation in which no conclusion can be reached regarding testing done due to one of many possible reasons (e.g., no results obtained, uninterpretable results obtained, no exemplar/standard available for testing).

Indigo dye

A blue-colored dye that is derived from several plant species and commonly used to dye denim for blue jeans. A known PCR inhibitor.


In forensic science, the process of attempting to associate an item of evidence with one and only one source.


A substance that interferes with or prevents the polymerase chain reaction.

Inner Cuticle Margin

The border between the cuticle and the cortex.

Intercalating dye

A chemical that can insert itself between the stacked bases at the center of the DNA double helix, possibly causing a frameshift mutation.

Internal Size Standard (ISS)

Specific DNA fragments of known sizes which are defined and used to size unknown fragments.


Written questions proposed to a party to which specific written responses (under oath) are required.

Internal testing

An internal test
is one that is created and administered by the laboratory itself.

Intimate Sample

An intimate sample is generally referred to a biological sample obtained from a source other than the mouth (saliva) and head (hair).

Irresolvable mixture

A DNA profile where multiple individuals have contributed biological material and no profile is more or less apparent than any other and the developed alleles cannot be isolated to a single source.

Isoamyl Alcohol

A chemical used in organic extractions to reduce the foaming of reagents, making it easier to detect the interface between the organic and aqueous phases.


Multiple forms of enzymes arising from genetically determined differences in primary structure. The term does not apply to those derived by modification of the same primary sequence.



John Doe Warrant

A warrant used when crime scene evidence yields a DNA profile but the individual corresponding to the DNA profile is unknown. In lieu of the suspect's name, the warrant will be filed as "John Doe" and cite the DNA profile.

Junk DNA

Stretches of DNA that do not code for genes; "most of the genome consists of junk DNA."

Juror nondisclosure

A prospective juror's failure or refusal to reveal something that either might be or is required to be revealed.

Jury instructions

An instruction given by the court to a jury at the conclusion of presentation of all evidence in a trial, and after the lawyers' closing arguments, to advise the jury of the law that applies to the facts of the case, and the manner in which they should conduct their deliberations.

Justice for All Act 2004

Provides for post-conviction DNA testing for federal prisoners with Actual Innocence claims for whom DNA testing may produce evidence of innocence. The act also creates grants to states to fund post-conviction DNA testing.




Any of the various sulphur-containing fibrous proteins that form chemical basis for keratinized epidermal tissues such as hair, nails, feathers, and horns of animals.


Hair that is closely curled or twisted.

Known samples

A DNA sample for which the source is known. These samples are generally obtained from the victim and/or suspected perpetrator of a crime, as well as from other persons whose DNA might be reflected when samples of the evidence are analyzed (could include a boyfriend, husband, or other third-party). These samples are also referred to as reference samples, since they serve as a reference to which the unknown DNA samples are compared with the goal of identifying the source of the unknown DNA samples.




The fine hairs found on the human fetus.

Latent print

A print impression that is not readily visible, made by contact with a surface.


The Local DNA Index System of CODIS, which uploads forensic and offender DNA profiles to the State DNA Index System, or SDIS.

Learned treatise

A book, publication, journal or any other professional, scientific, technical or specialized writing that is considered authoritative in a particular field.

Length heteroplasmy

The presence of mtDNA molecules that differ in length.

Likelihood ratio

The ratio of two probabilities of the same event under different hypotheses. In DNA testing often expressed as the ratio between the likelihood that a given profile came from a particular individual and the likelihood that it came from a random unrelated person. Note that in this case the likelihood of each event does not add to give 1 (100% likelihood) as it does not incorporate the possibility of error or that the profiles came from twins or other near relatives.

Linkage Equilibrium

When two or more genetic loci appear to segregate randomly in a given population. The genotypes appear randomly with respect to each other.


A large molecule containing a lipid and a carbohydrate.

Locard's Exchange Principal

States that every time someone enters an environment, something is added to and removed from it. The principle is sometimes stated as "every contact leaves a trace," and applies to contact between individuals as well as between individuals and a physical environment.

Local (LDIS)

The Local DNA Index System of CODIS which uploads forensic and offender DNA profiles to the State DNA Index System, or SDIS.

Locus (pl. loci)

The specific physical location of a gene on a chromosome.

Looped Cuticle

A looped cuticle is a condition in which the distal edges of the cuticle scales are curved from or cup toward the hair shaft.

Low copy number

Refers to examination of less than 100pg (picograms) of input DNA.




A term that describes characteristics large enough to be perceived without magnification; in forensic hair examination, this typically applies to unmounted hairs.


The height of the image divided by the height of the object. The apparent enlargement of an object by an optical instrument.

Major contributor profile

A DNA profile where multiple individuals have contributed biologic material and one individual's DNA profile is more apparent.

Malpractice cause of action

When brought against an expert witness, this action will protect and compensate injured individuals as well as deter future misconduct. It will ensure "quality control" of expert opinions by encouraging experts to be careful and accurate.


Pieces of DNA sequence of known locations on chromosomes that are used to identify the specific genetic variations an individual possesses.


Genetic profiles are said to "match" when they have the same allele designations at every loci.


Relevant and significant in a lawsuit (i.e., material evidence), as distinguished from evidence that is totally irrelevant or of such minor importance that the court will ignore it, rule it immaterial if there are objections, or not allow lengthy testimony on such a matter.


The mean of sample is calculated by taking the sum of all data values and dividing by the total number of data values.

Measurement scale

An object showing standard units of length (e.g., ruler) used in photographic documentation of an item of evidence.


Towards the long axis of the hair.


A series of air- or fluid-filled cells along the central axis of the hair.

Medullary Continuity

The continuous or discontinuous nature of the medulla.


The pigment occurring in plants, animals, and protista. It is responsible for skin and hair pigmentation. Two forms of melanin, eumelanin and phaeomelanin, determine the color of human hair. 

Melting Temperature Tm

The temperature at which one-half of a particular DNA duplex will dissociate and become single strand DNA.

Microbial Epidemiology

microbial: relating to a microbe or microbes; epidemiology: the study or the distribution and determinants of health-related states or events in specified populations, and the application of this study to control health problems.   


An instrument consisting essentially of a tube 160 mm long, with an objective lens at the distant end and an eyepiece at the near end. The objective forms a real aerial image of the object in the focal plane of the eyepiece where it is observed by the eye.


A term for objects which are too small to be resolved by the unaided eye.

Midshaft Region

The region of the hair between the proximal and distal ends.

Minisatellite Variant Repeat (MVR)

Tandem repeats of a short (10- to 100-bp) DNA fragments spanning several hundred to several thousand base pairs.


A fact or situation that does not justify or excuse a wrongful act or offense but that reduces the degree of culpability and thus may reduce the punishment.

Mitochondrial DNA (mtDNA)

The DNA found in the many mitochondria found in each cell of a body. The sequencing of mitochondrial DNA can link individuals descended from a common female ancestor.


An archaic anthropological term designating peoples originating from Asia, excluding the Indian subcontinent but including the Native Americans.


Monilethrix is a hair disorder that results in periodic nodes or beading along the length of the hair with intervening, tapering constrictions that are not medullated.


Having no practical significance.


Shape, form, external structure, or arrangement, especially as an object of study or classification

Motion in limine

A certain type of motion which may be submitted to the judge during the pretrial proceedings or during the trial to limit the admissibility of evidence. The motion in limine requests that certain types of evidence not be allowed at trial, for various prejudicial, irrelevancy or constitutional reasons. Before the trial, the judge rules on these pretrial motions to determine whether the evidence in question will be admissible during the trial.

mtDNA types

A mtDNA type is the sequence of a region of mtDNA. Common sources of mtDNA are hairs, skeletal remains, and teeth.


A system for analyzing several loci at once.


Damaged or changed DNA anywhere along the DNA strand.



National DNA Index System (NDIS)

Authorized by the DNA Identification Act of 1994, the FBI administers this national index. NDIS compares DNA profiles associated with a crime scene to DNA profiles collected from known convicted offenders, as well as to other crime scene profiles. When the DNA profiles are uploaded to NDIS, they are searched against the other DNA profiles submitted by other participating states.

National Research Council (NRC)

The National Research Council was convened in 1989. In 1996 the NRC filed the  report The Evaluation of Forensic DNA Evidence (referred to as NRC II). This document revised and expanded the initial report written in 1992 (NRC I). These recommendations are recognized by U.S. courts.


An archaic anthropological term designating most of the peoples originating from Africa.

No results

A situation in which no interpretable results are obtained from testing a DNA sample. A finding of no results can be due to the absence of DNA, insufficient DNA, or substances that inhibit the PCR process, among others.


Inconsistencies in laboratory practices that do not meet accreditation standards.


An individual is eliminated as the source of a biological sample. This occurs when one or more types from a specific location in the DNA of a known individual are not present in the type(s) for that specific location in the DNA obtained from an evidence sample.

Nonporous Container

Packaging through which liquids or vapors cannot pass (e.g., glass jars or metal cans).

Nuclear DNA

The DNA found in the nucleus of a cell.


One of the several classes of enzymes that degrade nucleic acid. An enzyme that can degrade DNA or RNA by breaking phosphodiester bonds.


A nucleus or occurring in the nucleus.


The cellular organelle that contains most of the genetic material.

Numerical aperture

A measure of the information-collecting ability of a microscope optic. The greater the NA, the better the resolving ability. It is a measure of the light-gathering capacity of the lens system and determines its resolving power and depth of field.



Objective test

A test which having been documented and validated is under control so that it can be demonstrated that all appropriately trained staff will obtain the same results within defined limits. These defined limits relate to expressions of degrees of probability as well as numerical values.

Off Ladder (OL) Alleles

Alleles that size outside allele categories represented in the ladder.

Offender Hit

A CODIS match between a crime scene profile and an offender profile.

Offender Index

DNA profiles developed from qualifying offenders and uploaded into CODIS are maintained in the offender index of the database.

Ohm's Law

The amount of current flowing in a circuit made up of pure resistances is directly proportional to the electromotive forces impressed on the circuit and inversely proportional to the total resistance of the circuit.


A molecule usually composed of 25 or fewer nucleotides; used as a DNA synthesis primer.

Optical Density (OD)

Synonymous with absorbance. Absorbance is the logarithm of the ratio of incident to transmitted radiant power through a sample.

Outer Cuticle Margin

The border of the outermost edge of the cuticle.

Ovoid Bodies

Oval-shaped heavily pigmented bodies that may occur in the hair cortex.



Partial profile

DNA evidence that does not yield identifiable results in all 13 core loci.

Partially degraded DNA

Forensic DNA evidence exposed to environmental conditions that may prevent it from yielding a usable profile.

Paternal inheritance

Genetic material which is inherited from one's father; for example, the possibility that mtDNA can be inherited from one's father.

Paternity or System Index (PI or SI)

A statistic that compares the likelihood that a genetic marker (allele) that the alleged father passed to the child to the probability that a randomly selected unrelated man of similar ethnic background could pass the allele to the child.

PCR Inhibitors

A substance that interferes with the Polymerase Chain Reaction (PCR) process. Examples of PCR inhibitors include dyes, soil, chemicals, and heme (hemoglobin).

Peripheral Region

The peripheral region is the portion of the hair toward the outermost areas of the hair, including the cuticle and the outer areas of the cortex, distant from the medullary or central region.

Personal Protective Equipment (PPE)

Articles such as disposable (latex) gloves, masks, shoe covers, and eye protection that are utilized to provide a barrier to keep biological or chemical hazards from contacting the skin, eyes, and mucous membranes and to avoid contamination of the crime scene. 

Personal Service

Delivering a summons, complaint, notice to quit tenancy or other legal document which must be served by handing it directly to the person named in the document. The delivery of legal notice to a party in a case. Notice consists of a copy of the complaint and a summons to appear in court, which must be served by handing it directly to the person named in the document. Also known as service of process. Service of Process is the delivery of legal notice to a party in a case. Any party who is being sued is entitled to advance notice of the suit. Notice consists of a copy of the complaint and a summons to appear in court.


A chemical used in organic extraction. Polysaccharides and proteins are soluble in phenol, allowing for their separation from DNA. C6H5OH.


The detectable outward manifestations of a specific genotype; the physical characteristics of a living object.


Coloration or discoloration by formation or deposition of pigment in the tissues. In a forensic hair examination, the description of the aggregation, distribution, and density of pigment granules.

Pili Annulati

Pili annulati is a hair disorder that results in ringed or banded hair, alternating bright and dark bands in the hair shaft. The dark bands are a manifestation of the abnormal air spaces in the cortex.

Pili Bifurcati

A genetic hair disorder characterized by two hairs joined at the shaft along their entire length.

Pili Torti

A genetic hair disorder characterized by the hair shaft being flattened and twisted 180 degrees numerous times along its axis. It is usually found at irregular intervals along the shaft.

Polymerase Chain Reaction (PCR)

A process used in DNA identification testing in which one or more specific small regions of the DNA are copied using a DNA polymerase enzyme so that a sufficient amount of DNA is generated for analysis.


Variable, more than one kind.


Variations in DNA sequences in a population that are detected in human DNA identification testing.


A stretch of adenine and/or guanine.


A stretch of cytosine and/or thyamine.


FBI CODIS software program used to perform statistical DNA match estimates.

Population Genetics

The study of the distribution of genes in populations and of how the frequencies of genes and genotypes are maintained or changed.

Postmortem Root Banding

An opaque ellipsoidal band, composed of parallel elongated air spaces, which appear on the proximal portion of hair shafts from postmortem hairs, likely to be in the anagen growth phase.

Preliminary opinion

The first stage of an expert witness's opinion-forming process. Early judgments are made about a case on the basis of preliminary testing and/or evaluation of evidence, subject to later verification based on additional investigation.

Preliminary Report

An initial opinion or conclusion, preferably in verbal, unwritten form (for discovery and attorney work-product privilege purposes), reflecting still-open areas of inquiry and the unfinished nature of fact and evidence investigation and testing. Typically suggests elements or areas of further inquiry necessary for the expert to reach a final and more conclusive opinion.

Preferential Amplification

Imbalanced amplification or lack of amplification at a locus.

Presumptive Test

A screening test used to indicate the possible presence of the named body fluid.

Pretrial conference

A meeting of the parties to a case conducted prior to trial. The conference is held before the trial judge or a magistrate, a judicial officer who possesses fewer judicial powers than a judge. A pretrial conference may be held prior to trial in both civil and criminal cases. A pretrial conference may be requested by a party to a case, or it may be ordered by the court. Generally, the term pretrial conference is used interchangeably with the term pretrial hearing/meeting.

Pretrial hearing/meeting

See pretrial conference

Pretrial motions

Motions that are made before the actual trial. After the preliminary hearing and before a trial, the prosecutor and the defense team appear before the criminal court judge and make pretrial motions. These motions can be for varied reasons like certain evidence should be kept out of the trial or that certain persons must or cannot testify, or that the case should be dismissed altogether etc. Example of a pretrial motion is a motion to suppress evidence. A motion to suppress may be made to exclude a confession that the defendant alleges that he or she signed without reading his Miranda rights.


The tendency is for people to believe the most and the longest what they hear first.


A segment of DNA or RNA that is complementary to a given DNA sequence and that is needed to initiate replication by DNA polymerase.

Primer dimer

Formed by intermolecular interactions between the two primers (i.e., self-dimers and cross-dimers).


Those communications, written or verbal, between certain classes of persons which cannot be reached by the opposition in the dispute-resolution process.


The chance of observing a particular future event; a simple ratio of the number of observed events divided by the total number of possible events.

Probability calculations

Predictions based on small sampling of a larger population.

Probability of Exclusion

The probability that a random individual would be excluded as the source of analyzed DNA evidence.

Probability of inclusion

The probability that a random individual would be included as a potential source of analyzed DNA evidence.

Probability of Paternity

A formula that tests the hypothesis that the accused is the biological father of the child.

Probability of human conduct

People are expected to act in certain ways in light of given circumstances. When they do act as expected, they are believable. When they do not act as expected, they are not believable.


Tending to prove a particular proposition or to persuade one of the truth of an allegation. "Evidence should only be excluded if its probative value is outweighed by its prejudicial effect."


Defined nucleic acid (DNA or RNA) that can be used to identify, usually through autoradiography, specific DNA or RNA molecules bearing the complementary sequence.

Product rule

The product rule calculates the expected chance of finding a given STR (short tandem repeat) profile within a population by multiplying the frequency of occurrence of the combination of alleles (genotype) found at a single locus, by the frequency of occurrence of the genotype found at the second locus, by the frequency of occurrence, in turn, of each of the other genotypes at the remaining STR loci.

Proffering attorney

Attorney who has hired or subpoenaed the witness who will testify.

Proficiency Test

A proficiency test is a quality assurance measure used to monitor performance of an examiner.

Proficiency testing

A DNA proficiency test uses biological samples to assess a lab analyst's ongoing competency and the laboratory's ability to produce accurate results.


  1. To attempt to use the court expert's independent and neutral fact testimony about DNA testing to affirm and solidify the DNA evidence findings in the state's case against the defendant.
  2. Also, in criminal law, prosecution refers to the government attorney charging and trying the case against a person accused of a crime; a common term for the government’s or state’s side in a criminal case.


Protein that binds DNA in sperm, replacing histones and allowing chromosomes to become more highly condensed than possible with histones.

Proteinase K

An endolytic protease that cleaves peptide bonds at the carboxylic sides of aliphatic, aromatic, or hydrophobic amino acids. Proteinase K in the extraction buffer inactivates nucleases and aids in lysis of epithelial and white blood cells to free nuclear DNA.


A series of steps, processes or procedures usually followed in a scientific, technical, professional or specialized area.

Proximal End

The portion of the hair towards the root.


Specifically related to ABI Gene Scan® software, a peak seen in one color that is not due to the presence of DNA, but to incorrect compensation for the spectral overlap of the four dyes used in detecting multiple loci in one reaction. See also: Artifact



Quality Assurance (QA)

A program conducted by a laboratory to ensure accuracy and reliability of tests performed.

Quality Assurance Standards

The standards originated from the DNA Advisory Board and are maintained by the FBI; they place specific requirements on labs involved in forensic DNA analysis, both casework and convicted offender databasing. See the FBI's:
QAS for Forensic DNA Testing Laboratories
QAS for DNA Databasing Laboratories


Method used to determine the quantity of "x" in a given sample. In this context, it refers to the quantity of DNA in a sample and is usually reported as ng/µl.

Quantitative PCR (qPCR)

Sometimes referred to in forensic science as real-time PCR. An amplification process that detects and measures the accumulation of fluorescent dyes as the reaction progresses. The initial quantity of DNA in the sample is detected by monitoring the exponential growth phase of the reaction and measuring the cycle number at which the fluorescent intensity of the sample overcomes the background noise or threshold.

Questioned Sample

A sample recovered or collected, about which there are questions, for a forensic examination.



Racial group

A group of people defined by race, color, nationality, and ethnic or national origins.

Random match probability

The probability that the DNA in a random sample from the population has the same profile as the DNA in the evidence sample.

Randomly Amplified Polymorphic DNA Markers

Random amplification of polymorphic DNA. A method for identifying differences between genomes of different individuals by PCR with a single short (usually 10-base) primer, which will anneal with complementary sequence at undetermined positions in the genome.


The tendency is for people to believe what they hear last.

Reciprocal Discovery

Some jurisdictions enable a prosecutor by motion to request that the defense provide specific discovery material to the prosecution.

Recombinant DNA - 

Altered DNA resulting from the insertion into the chain, by chemical, enzymatic, or other biological means, of a sequence (a whole or partial chain of DNA) not originally (biologically) present in that chain.


The reversal of coupling phase I meiosis as gauged by the resulting phenotype. See also Recombinant DNA above.

Reference Samples

A standard/reference sample is material of a verifiable/documented source which, when compared with evidence of an unknown source, shows an association or linkage between an offender, crime scene, and/or victim (e.g., a carpet cutting taken from a location suspected as the point of transfer for comparison with the fibers recovered from the suspect's shoes, a sample of paint removed from a suspect vehicle to be compared with paint found on a victim's vehicle following an accident, or a sample of the suspect's and/or victim's blood submitted for comparison with a bloodstained shirt recovered as evidence).

Reflected light

Incident illumination (cf. transmitted light)


When light strikes a surface and then leaves at the same angle. Angle in=angle out. The production of an image by or as if by a mirror.

Relative fluorescence unit (RFU)

a unit of measurement used in electrophoreses methods employing fluorescence detection. Fluorescence is detected on the CCD array as the labeled fragments, separated in the capillary by electrophoresis, and excited by the laser, pass the detection window. The software interprets the results, calculating the size or quantity of the fragments from the fluorescence intensity at each data point.


The deflection from a straight path undergone by a light ray or energy wave in passing obliquely from one medium (as air) into another (as glass) in which its velocity is different, or the action of distorting an image by viewing through a medium.


A term defined as the tendency to make a fact of issue either more or less probable.

Representative Sample

A collection of hairs from a specific body area that encompasses the characteristics expressed in an individual's hair.

Request for admission

A discovery process by which one party requests the other party to admit that particular facts or circumstances are true or certain events actually occurred.

Request for production

A written request to a party to produce documents and other tangible items for copying or inspection.


A measurement of how well the smallest details of an image can be discerned. The process or capability of making distinguishable the individual parts of an object, closely adjacent optical images, or sources of light.

Restriction enzyme

A protein harnessed from bacteria that recognizes specific, short nucleotide sequences and cuts DNA at those sites.

Restriction fragment length polymorphism

- Variation in the length of a stretch of DNA; abbreviated RFLP.

Rules of Evidence

Rules that determine what is and is not admissible in various dispute-resolution processes. They may be enacted by the legislative bodies, determined by appellate decision or controlled by court order.


The root is the structure at the proximal end of a hair.




Failure to honor a personally served subpoena may result in a court-ordered fine or the forced surrender of the person. A witness who ignores, disregards or even forgets to honor a subpoena to appear and testify may be held in contempt of court.

Sanger Sequencing

A widely used method of determining the order of bases in DNA.


Also known as sodium lauroylsarcosine. A detergent used in DNA extraction.

Scientific method

The principles and empirical processes of discovery and demonstration necessary for scientific investigation. These processes generally involve the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to demonstrate the truth or falseness of the hypothesis, and a conclusion that validates or modifies the hypothesis.


Scales are plate-like structures composed of keratin that overlap to form the cuticle.


State DNA Index System containing the state-level DNA records uploaded from local laboratory sites within the state. SDIS is the state's repository of DNA identification records and is under the control of state authorities. The SDIS laboratory serves as the central point of contact for access to the National DNA Index System (NDIS). The DNA Analysis Unit I (DNAUI) serves as the SDIS laboratory for the FBI.


The fluid (ejaculate) that is released through the penis during orgasm. Semen is made up of sperm from the testicles and other fluid from other sex glands.

Sequence (or site) heteroplasmy

Presence of mtDNA molecules that have different nucleotides at the same address.


Determination of the order of base sequences in a DNA molecule.


The portion of a hair between the root and the tip.


In the context of trials, the isolation of a jury from the public, or the separation of witnesses to ensure the integrity of testimony. In a jury trial, a judge may choose to sequester the jurors, or place them beyond public reach. Jurors are moved into a hotel, kept under supervision 24 hours a day, denied access to outside media (TV and newspapers), and allowed only limited family contact. Jury sequestration is rare, and has two broad purposes: to avoid the accidental tainting of the jury, and to prevent others from intentionally tampering with jurors by bribe or threat. In witness sequestration, witnesses typically are ordered not to attend the trial, or follow accounts of it, until they are called to testify. This judicial order is intended to assure that the witnesses will testify concerning their own knowledge of the case without being influenced by testimony of prior witnesses.

Short Tandem Repeat (STR) typing

DNA analysis method which targets regions on the chromosome which contain multiple copies of an identical DNA sequence in succession.

Short Tandem Repeats (STR)

Multiple copies of a short identical DNA sequence arranged in direct succession in particular regions of chromosomes.


An asymmetrical cross-section.

Signal to Noise Ratio

A measure of signal strength relative to background noise.


Of the same substance or structure throughout; homogeneous; having a marked resemblance or likeness; of a like nature or kind.

Simple Sequence Repeats (SSR)

A sequence consisting largely of a tandem repeat of a specific k-mer (such as (CA)15). Many SSRs are polymorphic and have been widely used in genetic mapping.

SINE (Short INterspersed Element)

A type of small dispersed repetitive DNA sequence (e.g. Alu family in the human genome) found throughout a eukaryotic genome.

Single Nucleotide Polymorphisms (SNPs)

DNA sequence variations that occur at a single nucleotide (A,T,C,or G).

Single source profile

A DNA profile where only one individual has contributed biologic material.

Single-use Equipment

Items that will be used only once to collect evidence, such as biological samples, then discarded to minimize contamination (e.g., tweezers, scalpel blades, droppers).

Slot Blot

A technique for measuring the amount DNA or RNA. Samples are placed onto a hybridization membrane, fixed, and hybridized with a probe. Visualization techniques include use of a radioactive probe, chemiluminescence, or colorimetric based systems. The concentration of the samples is determined by comparing to standards of known concentrations.

Sodium Dodecyl Sulfate (SDS)

Also known as sodium lauryl sulfate (SLS). A detergent used in DNA extraction.


Referring to an area of the body.


The determination of the structure or quantity of substances by measuring their capacity to absorb light of various wavelengths.


Polyamines originally isolated from semen and can inhibit PCR. Found in ribosomes and living tissues.


Polyamines originally isolated from semen and can inhibit PCR. Found in ribosomes and living tissues.

Standard Operation Procedures (SOP)

A prescribed procedure to be followed routinely.

State (SDIS)


An agreement or concession made by parties in a judicial proceeding (or by their attorneys) relating to the business before the court; must be in writing unless they are part of the court record; "a stipulation of fact was made in order to avoid delay".

State SDIS

State DNA Index System containing the state-level DNA records uploaded from local laboratory sites within the state. SDIS is the state's repository of DNA identification records and is under the control of state authorities. The SDIS laboratory serves as the central point of contact for access to NDIS. The DNA Analysis Unit I (DNAUI) serves as the SDIS laboratory for the FBI.

Stochastic effects

Being or having a random variable.


A minor band or peak appearing one repeat unit smaller than a primary STR (short tandem repeat) allele. Occasionally, the repeat unit is larger than the primary allele.


A formal document that orders a named individual to appear before a duly authorized body at a fixed time to give testimony.

Subpoena duces tecum

A type of subpoena that compels the witness to produce documents, data or other physical evidence created or in his or her possession (such as hair, blood or saliva samples). It cannot be used to require oral testimony and ordinarily cannot be used to compel a witness to reiterate, paraphrase, or affirm the truth of the documents produced. Although frequently employed to obtain discovery during litigation, a subpoena duces tecum may not be used for a "fishing expedition" to enable a party to gain access to massive amounts of documents as a means of gathering evidence. The subpoena should be sufficiently definite so that a respondent can identify the documents sought without a protracted or extensive search. Moreover, a person ordinarily is required to produce only documents in her possession or under his or her control and supervision. A subpoena duces tecum may be used to compel the production of the papers and books of a business, however. A subpoena duces tecum is not limited to parties to a lawsuit but may also be used for others who have relevant documents. In the absence of a valid excuse, an individual served with a subpoena duces tecum must produce the items sought, although a subordinate may comply instead. A subpoena duces tecum may be challenged by a motion to quash, modify, or vacate the subpoena or by a motion for a protective order. The subpoena might not be permitted if alternative methods for obtaining the information sought are available. Determining whether a subpoena duces tecum should be enforced is a discretionary matter within the judgment of the court. In Latin subpoena duces tecum means "appear and bring with you." Generally, in order for a subpoena duces tecum to compel the production of anything, other than a witness's appearance, the subpoena duces tecum must be properly served.


Any background material upon which biological sample has been deposited (e.g., clothing, glass, wood, upholstery).


Liquid portion remaining after centrifugation or precipitation of a sample.


Scientific Working Group of DNA Analysis and Methods, formerly called TWGDAM (Technical Working Group on DNA Analysis and Methods).



Tannic Acid

A naturally occurring compound used for tanning animal hides into leather. A known PCR inhibitor.

Taq Polymerase

A heat-stable DNA polymerase isolated from the bacterium Thermus aquaticus, used in PCR.

TE Buffer

A commonly used buffer in Molecular Biology, especially in procedures involving DNA. It is called "TE" buffer because it contains Tris and EDTA.


The last phase of the hair growth cycle when the hair root becomes a bulbous shaped root.

Terminal hair

Long, coarse, generally pigmented hairs, sometimes with medullation, representing the final state of differentiation of human hair. (cf. vellus, lanugo)


A means of analysis, examination or diagnosis.


The process of conveying information from a witness to a judge, jury, arbitration or other hearing panel.

Thermal Cycler

An instrument used to perform the polymerase chain reaction (PCR).

Theta Correction

A theta adjustment is a mathematical correction applied to a frequency calculation when both alleles at a locus are the same (known as a homozygous state). It is not applied when alleles are different at a locus (known as a heterozygous state). This correction adjusts the frequency slightly upwards to account for the presence of subpopulations in a general population database that might otherwise cause the genotype frequency to be underestimated at that locus.

Third Party Defense Motion

A motion filed by the prosecution to preclude the defense from asserting that DNA evidence is derived from a third party, possibly a relative of the accused.


The point that must be exceeded to begin producing a given effect or result or to elicit a response.

Threshold value

A relative fluorescent unit (RFU) value that must be exceeded to make an allele call. This value will vary among laboratories.


The most distal end of a hair's shaft.

Trace evidence

Physical evidence that results from the transfer of small quantities of materials (e.g., hair, textile fibers, paint chips, glass fragments, gunshot residue particles).


Allowing the passage of light, yet diffusing it so as not to render bodies lying beyond clearly visible; semi-transparent.

Transmitted light

Illumination which passes through a medium.


Having the property of transmitting light, so as to render bodies lying beyond completely visible.

Trial (jury)

A civil or criminal trial in which a jury decides any disputed issues of fact. The number of jurors is usually 12 in a criminal trial; the number varies from state to state in a civil trial.


The study of the structure, functions, and diseases of the hair.


A condition characterized by apparent or actual knotting of the hair.


A disease condition characterized by longitudinal splitting or fraying of the hair shaft.

Trichorrhexis Invaginati

A genetic disease characterized by a segment of bulbous, dilated hair being enfolded into a concave hair terminal, recalling the appearance of a bamboo node. If the hair breaks at the bulbous end, the hair has a "golf tee cup" end.

Trichorrhexis Nodosa

A condition characterized by the formation of nodes, and in extreme cases, the hair is weaker at the node and is subject to breakage.


A condition characterized by brittle hair with a transverse crack or a clean break.

Trier of Fact

The judge, jury, administrative body, board, or arbitration panel that determine(s) the factual issues of the controversy in the dispute-resolution process.


An abbreviation for tris (hydroxymethyl)methylamine, also known as tris(hydroxymethyl)aminomethane. It is widely used in biochemistry as a buffer salt.




Existing or being everywhere, widespread


Changes in diameter along the length of the hair shaft that result from changes in cross-sectional area. This can give the hair a wavy appearance.


Results which might be reported by the laboratory when alleles can not be interpreted.

Upper Bound Frequency Estimates

an estimate of the percentage of individuals who could be potential contributors of a mtDNA profile.

UV light source

Use of an ultraviolet light source to enhance or visualize potential items of evidence (fluids, fingerprints, clothing fibers, etc.). The light will cause possible biological stains to change color or fluoresce, assisting in the location process.




The process of extensive and rigorous evaluation of DNA methods before acceptance for routine use.

Variable Number of Tandem Repeats (VNTRs)

Repeating units of a DNA sequence; a class of RFLPs (restriction fragment length polymorphism); abbreviated VNTR.


A measure of the spread of a distribution about its average value.


A dissimilarity in the commonly occuring sequence of a gene.


Short, fine, unmedullated hairs spread more or less uniformly over the body. 4 (Harding and Rogers, 1999).

Virtual Image

An image (as seen in a plane mirror) formed of points from which divergent rays (as of light) seem to emanate without actually doing so. It does not exist physically.

Voir dire

In a jury trial, the jury is selected by the parties through a process called voir dire, where the judge or parties ask jurors questions in order to determine their biases and opinions. (Each side gets to reject a certain number of potential jurors.)




An initial assessment conducted by carefully walking through the scene to evaluate the situation, identify potential evidence, and determine resources required. It can also be a final survey conducted to ensure the scene has been effectively and completely processed.


A hair shaft form with curvature that changes its direction to produce a sinuous wave form and does not curve back upon itself to form a circle.

Working distance

Distance between the front vertex of a lens and the object.




Short tandem repeats located on the Y chromosome.