A.F.I.S. - 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.
Adenosine Triphosphate (ATP) - Main source of energy for biochemical reactions within the cell.
Allele - 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 — The proportion of one allele relative to all alleles at a specific chromosomal location in a 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.
Amelogenin - 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.
Amplicons - Amplified DNA fragments.
Amplification - 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 or variations in DNA. DNA first undergoes restriction enzyme digestion, and a subset of DNA fragments is then selected for PCR amplification and visualization.
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.
“Authorised person” means in reference to —
(i) finger-prints, any police official in the performance or his or her official duties; or
(ii) the NDDSA (National DNA Database of South Africa), the police officer commanding the Division: Criminal Record and Forensic Science Service within the South African Police Service or his or her delegate
Autosomal chromosomes - Chromosomes which are not sex chromosomes.↑ Back to top
Base Pairing — Adenosine (A),Thymine (T), Cyotosine (C) and Guanine (G) are molecular building blocks of DNA that only join together in specific "base" pairs, e.g., A only pairs with T, and C only pairs with G.
Baseline - Residual signal associated with an instrument's blank response.
Bases - The four building blocks of DNA are called bases. The building blocks or nucleotides, are Cytosine, Guanine, Thymine, Adenine and are commonly referred abbreviated as C, G, T and 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.
Biallelic — A term pertaining to two different forms of a gene (allele) at a particular chromosomal location, e.g. single nucleotide polymorphisms display two alternate genetic sequences and are said to be biallelic.
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).
Boundaries - The perimeter or border surrounding potential physical evidence related to the crime.
Buffer - Chemical solution that maintains a relatively constant pH even with the addition of strong acids or bases.↑ Back to top
Cambridge Reference Sequence (CRS) - A "master template" of the HVR-1 region of mitochondrial DNA.
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
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.
Cathode - A negatively charged electrode.
Cation - Positively charged ion. (e.g., K+, Na+, NH4+)
Caucasoid - Caucasoid is an archaic anthropological term designating the peoples originating from Europe and the Indian subcontinent.
Cell - The smallest component of life capable of independent reproduction and from which DNA is isolated for forensic analysis.
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.)
Chemiluminescence - 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.
Chloroform - A chemical used in organic extraction. When used with phenol, promotes a sharp interface between the organic and aqueous layers.
Chromosome - The biological structure by which hereditary information is physically transmitted from one generation to the next. Located in the cell nucleus, each chromosome consists of a tightly coiled thread of DNA with associated proteins and RNA. The genes are arranged in linear order along the DNA molecule.
Clean/sanitize - The process of removing biological and/or chemical contaminants from tools and/or equipment.
Collect/collection - The process of identifying, documenting, gathering, and packaging or retaining physical evidence.
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.
Competency - The combination of demonstrated knowledge, skills, and abilities.
Competency Test - A test given during training to assess the ability of a trainee.
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.
Contamination - The undesirable transfer of material to physical evidence (DNA) from another source.
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.
Controls - Tests designed to demonstrate that a procedure worked correctly and performed in parallel with experimental samples.
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.
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 (replicate copies of the target DNA sequence) have accumulated.
Cytoplasm - The viscid, semifluid matter contained within the plasma membrane of a cell, excluding the nucleus.↑ Back to top
Degenerate Primer - A PCR primer sequence is called degenerate if some of its positions have several possible bases.
Degradation - The fragmenting, or breakdown, of DNA by chemical or physical means.
Denaturation - Separation of the two strands of a DNA double helix.
Deposition - The taking and recording of testimony of a witness under oath before a court reporter in a place away from the courtroom before trial.
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.
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).
Dissimilar - Not similar or alike; different in appearance, properties, or nature; unlike.
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 used 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 mixtures - A sample that contains the DNA of more than one individual.
DNA Profile (sometimes referred to as a DNA fingerprint) - The result of determining the relative sizes of repeated DNA sequences at several locations on an individual’s chromosomes. Each person (except identical twins) has a unique DNA profile and DNA profiling can thus be used to discriminate between unrelated individuals, such as in the context of the National DNA Database.
Documentation - 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.↑ Back to top
Electropherogram - The graphic representation of the separation of molecules by electrophoresis or other means of separation.
Electrophoresis - A method of separating large molecules (such as DNA fragments) from a mixture of similar molecules. An electric current is passed through a medium and molecules separate according to their electrical charge and size. Separation of DNA markers or fragments is based on these differences.
Elimination/Reference samples - A term used to describe a sample of known source taken for comparison purposes.
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).
Evidence - Something that can help identify the persons responsible for a crime, items used to establish an element of crime or to 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.
Excluded - Two samples cannot have come from the same source.
Exclusion - 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.
Exogenous DNA - DNA originating outside an organism that has been introduced into the organism.
Exonuclease - 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.
Expected Heterozygosity - Mean value of all the expected allelic frequencies, for all loci in a sample.
Expert System - A software program or set of software programs designed to rapidly process data without human intervention.
External testing - An external test is one that is created and administered by an outside agency.↑ Back to top
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.
Forensic Hit — A match between two or more crime scene profiles.
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.
Fractions - The result of a 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).
FSL - Forensic Science Laboratory
FSS - Forensic Science Services (UK)↑ Back to top
Gene - The basic unit of heredity; a functional sequence of DNA in a chromosome.
Genetic loci — Specific locations in the genetic material of an organism where certain DNA sequences can be found.
Genetics - The study of the patterns of inheritance of specific traits.
Genome - All the genetic material contained in the chromosomes of a particular organism; its size is generally given as its total number of base pairs.
Genotype - The genetic constitution of an organism, as distinguished from its physical appearance (its phenotype). The designation of the two alleles at a particular locus in one individual is referred to as their genotype.↑ Back to top
Haplotype - A way of denoting the collective genotype of a number of closely linked loci on a chromosome.
Hardy-Weinberg (Equilibrium) - In a large random mating population, not subjected to excessive selection or mutation, the gene and genotype frequencies will remain constant over time. For a single allele pair where p is the frequency of the A allele and q is the frequency of the a allele, and p? is the frequency of genotype AA, q? is the frequency of aa, and 2pq is the frequency of Aa, the sum of the genotypic frequencies, p?+2pq+q? will be equal to one when the population is in equilibrium
Heredity - The transmission of characteristics from one generation to the next.
Heteroplasmy - The presence of more than one mitochondrial DNA type within a single individual.
Heterozygosity - The probability that a given loci will be heterozygous in a randomly selected individual; having two different alleles at one locus.
Heterozygous - If two alleles are different at one locus, the person is heterozygous at that genetic location.
Histone - A type of basic protein that forms the unit around which DNA is coiled in the nucleosomes of eukaryotic chromosomes.
HLA DQ-alpha - A highly variable or 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.
Homozygous - If two alleles at a locus that are identical or indistinguishable, the person is homozygous at that genetic location.
Humic - An organic residue of decaying organic matter.
Hypervariable - 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.↑ Back to top
Immunoglobulin - 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.
Included - 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 genetic types from a specific location in the DNA of a known individual are also present in the genetic types for that specific location in the DNA obtained from an evidence sample.
Inconclusive - 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.
Individualization - In forensic science, the process of attempting to associate an item of evidence with one and only one source.
Inhibitors - A substance that interferes with or prevents a reaction such as the polymerase chain reaction.
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 DNA fragments of unknown length.
Internal testing - An internal test is one that is created and administered by the laboratory itself.
Intimate Sample —
(i) a sample of blood, semen or any other tissue fluid, urine or pubic hair;
(ii) a dental impression;
(iii) a swab taken from a person’s body orifice other than the mouth; or
(iv) a combination of these.
Non-Intimate Sample —
(i) a sample of hair other than pubic hair;
(ii) a sample taken from a nail or from under a nail;
(iii) a swab taken from the mouth (buccal swab);
(iv) a blood finger prick; or
(v) a combination of these.
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.
Isoenzyme - 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.↑ Back to top
Junk DNA - Stretches of DNA that do not code for genes; "most of the genome consists of junk DNA."↑ Back to top
Keratin - Any of the various sulphur-containing fibrous proteins that form the chemical basis for keratinized epidermal tissues such as hair, nails, feathers, and horns of animals.
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.↑ Back to top
Latent print - A print impression that is not readily visible, made by contact with a surface.
Length heteroplasmy - The presence of mitochondrial DNA 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.
Lipopolysaccharides - A large molecule containing a lipid and a carbohydrate.
Locus (pl. loci) - The specific physical location of a gene on a chromosome.
Low copy number - Refers to examination of less than 100pg (picograms) of input DNA.↑ Back to top
Macroscopic - A term that describes characteristics large enough to be perceived without magnification; in forensic hair examination, this typically applies to unmounted hairs.
Magnification - 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.
Marker - DNA sequences occurring at known locations on chromosomes. Markers are used to identify the specific genetic variations an individual possesses as well as differences between individuals in a population.
Match - Genetic profiles are said to "match" when they have the same allele designations at every loci.
Mean - 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.
Melanin - 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.
Microscope - 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.
Microscopic - A term for objects which are too small to be resolved by the unaided eye.
Minisatellite Variant Repeat (MVR) temperature - The temperature at which one-half of a particular DNA duplex will dissociate and become single strand DNA.
Mitochondrial DNA (mtDNA) - The DNA located 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.
Mongoloid - An archaic anthropological term designating peoples originating from Asia, excluding the Indian subcontinent but including the Native Americans.
Morphology - Shape, form, external structure, or arrangement, especially as an object of study or classification
mtDNA types - A mtDNA type is the sequence of a region of mitochondrial DNA. Common sources of mtDNA are hairs, skeletal remains, and teeth.
Multiplexed - A system for analyzing several genetic loci at once.
Mutation - Damaged or changed DNA anywhere along the DNA strand.↑ Back to top
NDDSA - The National DNA Database of South Africa, established in terms of section 17H of the South African Police Service Act.
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.
Non-conformances - Inconsistencies in laboratory practices that do not meet accreditation standards.
Nonmatch - An individual is eliminated as the source of a biological sample. This occurs when one or more genetic 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.
Nucleases - One of the several classes of enzymes that degrade nucleic acid. An enzyme that can degrade DNA or RNA by breaking phosphodiester bonds.
Nucleated - A nucleus or occurring in the nucleus.
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.↑ Back to top
Objective test - A test which having been documented and validated is controlled 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 whose fragment size is outside the allele categories represented in the allelic ladder.
Offender Hit — A match between a crime scene profile and an offender profile.
Offender Index - DNA profiles developed from qualifying offenders and uploaded into THE NATIONAL DNA DATABASE are maintained in the offender index of the database.
Oligonucleotides - 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.↑ Back to top
Partial profile - DNA evidence that does not yield identifiable results in all loci under analysis.
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.
Paternity or System Index (PI or SI) - A statistic that compares the likelihood that a genetic marker (allele) was passed to the child by the alleged father with 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).
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.
Phenol - A chemical used in organic extraction. Polysaccharides and proteins are soluble in phenol, allowing for their separation from DNA.
Phenotype - The detectable outward manifestations of a specific genotype; the observable physical characteristics of a living individual.
Pigmentation - 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.
Point Of Entry (POE) Ð The place that the perpetrator used to gain entry to the crime scene, for example a broken window or a forced open door. It is likely that there will be forensic evidence at the POE and the site must be treated as a priority when considering which areas of the crime scene to preserve.
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.
Polymorphic - Variable, more than one kind.
Polymorphism - Variations in DNA sequences in a population that are detected in human DNA identification testing.
Polypurine - A stretch of DNA consisting of the nucleotide bases adenine and/or guanine.
Polypyrimidine - A stretch DNA consisting of the nucleotide bases cytosine and/or thymine.
Population Genetics - The study of the distribution of genes in populations and of how the frequencies of genes and genotypes are maintained or changed over time.
Preferential Amplification - Imbalanced amplification or lack of amplification of DNA at a locus.
Presumptive Test - A screening test used to indicate the possible presence of a particular body fluid.
Primer - 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).
Probability - 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.
Probe — A defined nucleic acid (DNA or RNA) that can be used to identify an individual, usually through autoradiography. Specific DNA or RNA molecules bearing the complementary sequence to the DNA sequence under analysis.
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.
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 laboratory analyst's ongoing competency and the laboratory's ability to produce accurate results.
Protamine - 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.↑ Back to top
Quality Assurance (QA) - A program conducted by a laboratory to ensure accuracy and reliability of tests performed.
Quality Assurance Standards - The standards that place specific requirements on laboratories involved in forensic DNA analysis. This includes both casework and convicted offender databasing.
Quantitation - 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.↑ Back to top
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 sequences at undetermined positions in the genome.
Recidivism - A tendency to relapse into a previous condition or criminal behaviour.
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 DNA sequence (a whole or partial chain of DNA) not originally (biologically) present in that chain.
Recombination — The production of gene combinations not found in the parents arising from the assortment of chromosomes and crossing over between chromosomes during meiosis.
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)
Reflection - 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.
Refraction - 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.
Resolution - 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 (RFLP) — Variation in the banding patterns of DNA fragments generated by restriction enzymes.↑ Back to top
Sanger Sequencing - A widely used method of determining the order of nucleotide bases in DNA.
Sarkosyl - Also known as sodium lauroylsarcosine. A detergent used in DNA extraction.
Semen - 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 — A cellular condition in which two genetically different DNA sequences occur in an organelle (usually mitochondria).
Sequencing - Determination of the order of base sequences in a DNA molecule.
Shaft - The portion of a hair between the root and the tip.
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.
Signal to Noise Ratio - A measure of signal strength relative to background noise.
Similar - Of the same substance or structure throughout; homogeneous; having a marked resemblance or likeness; of a like nature or kind.
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.
Somatic - Referring to an area of the body.
South African Police Service Act - The South African Police Service Act, 1995 (Act No. 68 of 1995)
Spectrophotometry - The determination of the structure or quantity of substances by measuring their capacity to absorb light of various wavelengths.
Speculative Search means that the finger-prints or intimate samples or non-intimate samples or the information derived from such samples taken, by the police service, may for purposes related to the prevention or detection of crime, the investigation of an offence or the conduct of a prosecution, be checked by an authorized person, against -
(i) in the case of fingerprints, the fingerprint databases of the South African Police Service, the Department of Home Affairs or the Department of Transport; or
(ii) in the case of intimate samples or non-intimate samples, or the information derived from such samples, the NDDSA.
Spermidine (spermine) - Polyamines originally isolated from semen and that can inhibit PCR. Found in ribosomes and living tissues.
Standard Operation Procedures (SOP) - A prescribed procedure to be followed routinely.
Stochastic effects - Being or having a random variable.
Stutter - 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.
Substrate - Any background material upon which a biological sample has been deposited (e.g., clothing, glass, wood, upholstery).
Supernatant - Liquid portion remaining after centrifugation or precipitation of a sample.
SWGDAM - Scientific Working Group of DNA Analysis and Methods, formerly called TWGDAM (Technical Working Group on DNA Analysis and Methods).↑ Back to top
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.
Telogen - 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)
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.
Threshold - 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 before an allele can be correctly identified. This value will vary among laboratories.
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) which may link an offender with a scene if they can be identified as having originated in the same place or as being from the same source.
Translucent - 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.
Transparent - Having the property of transmitting light, so as to render bodies lying beyond completely visible.
Trichology - The study of the structure, functions, and diseases of the hair.
Tris - An abbreviation for tris (hydroxymethyl)methylamine, also known as tris(hydroxymethyl)aminomethane. It is widely used in biochemistry as a buffer salt.↑ Back to top
Uninterpretable - 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 mitochondrial DNA 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.↑ Back to top
Validation - 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 that vary in number between different alleles.
Variance - A measure of the spread of a distribution about its average value.
Variant - A dissimilarity in the commonly occuring sequence of a gene.
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.↑ Back to top
Walk-through - 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.
Working distance - Distance between the front vertex of a lens and the object.↑ Back to top
Y-STR - short tandem repeats located on the Y chromosome.↑ Back to top