Glossary

A : B : C : D : E : F : G : H : I : J : K : L : M : N : O : P : Q : R : S : T : U : V : W : X : Y : Z

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2p rule - The NRCII report recommends using this approach for dealing with homozygotes.

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Alternate Light Source (ALS) - Equipment that produces high intensity light at various wavelengths; used to enhance or visualize potential items of evidence (fluids, fingerprints, clothing fibers, etc.).
Adenosine Triphosphate (ATP) - Main source of energy for biochemical reactions within the cell.
Allele calls -
Allelic drop-out - Failure to detect an allele in a sample or failure to amplify an allele during PCR.
Allelic ladder - Comprised of DNA fragments that represent common alleles at a locus.
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 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 - Proportion of a particular allele among the chromosomes carried by individuals in a population.
Alu - 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.
Amplicons - Amplified DNA fragments.
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.
Annealing Temperature T_a - An annealing temperature is approximately 5°C below the lowest melting temperature Tm of the pair of primers is used.
Anode - A positively charged electrode.
Antigen - A molecule whose shape triggers the production of antibodies (immunoglobulins) that will bind to the antigen. A foreign substance capable of triggering an immune response in an organism.
Autosomal DNA - The genetic material found in any nucleated cell, excluding sex chromosomes.

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Baseline - Residual signal associated with an instrument’s blank response.
Bayesian probability - System of probability based on beliefs in which the measure of probability is continuously revised as available information changes.
Biallelic - System of probability based on beliefs in which the measure of probability is continuously revised as available information changes.
Bovine serum albumin (BSA) - Protein fraction of serum isolated from the bovine family (i.e. cow, ox, buffalo).

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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).
Cathode - A negatively charged electrode.
Capillary Electrophoresis (CE) - DNA separation techniques that use silica capillaries (or narrow tubes) containing a polymer solution, through which the negatively charged DNA molecules migrate under the influence of a high voltage electric field.
Cation - Positively charged ion. (e.g. K⁺, Na⁺, NH₄⁺)
Chaotropic - 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.
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.
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.
CODIS - Acronym for Combined DNA Index System. A collection of databases of DNA profiles of forensic interest. Contributions are made through approved laboratories and the data are maintained by the FBI.
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.
Counting Method -
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.

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Degenerate Primer - A PCR primer sequence is called degenerate if some of its positions have several possible bases.
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.
Discriminating Power - The ability of a blood grouping technique to differential between individuals selected at random. This can also be applied to other analytical techniques in forensic science.
Dithiothreitol (DTT) - Reducing or deprotecting agent for thiolated DNA. (1,4-Dicaptomercapto-2,3-butanediol; formula is C4H10O2S2)

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Electropherogram - A recording of the separated components of a mixture produced by electrophoresis.
Electrophoresis - A recording of the separated components of a mixture produced by electrophoresis.
Ethnicity - 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.
Exclusion - The elimination of an individual 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.
Expected Heterozygosity - Mean value of all the expected values found for all loci in a sample.
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.

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No terms in this section

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Genotype - The genetic makeup of an individual.

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Haplotype - is a set of closely linked genetic markers present on one chromosome which tend to be inherited together (not easily separable by recombination). Another way to think about it is that a haplotype is half of a genotype.
Haptoglobin - A protein present in blood serum that combines with hemoglobin to form a complex that is rapidly removed from the circulation by the liver.
Heme - The deep red, non-protein, ferrous component of hemoglobin. C₃₄H₃₂FeN₄O₄
Heteroplasmy - The presence of more than one mtDNA type within a single individual.
Heterozygous - Having two different alleles at the same locus.
Histone - 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.
Homozygous - Having two of the same alleles at the same locus.
Humic - An organic residue of decaying organic matter.
HLA DQ-alpha - A polymorphic gene 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.
Hydroxyquinoline - A bicyclic aromatic compound, which when added to phenol turns the aqueous phase orange, making it easier to differentiate in the organic extraction. See figure to the right.

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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.
Inclusion - The inability to exclude an individual as the 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 type(s) for that specific location in the DNA obtained from an evidence sample.
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.
Inhibitors - A substance that interferes with or prevents the polymerase chain reaction.
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.
Intercalating Dye - A chemical that can insert itself between the stacked bases at the centre 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.
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.

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Leukocyte - White blood cell.
Likelihood Ratio - The ratio of two probabilities of the same event under two different hypotheses.
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 (LCN) - Refers to the examination of less than 100 picograms of input DNA.

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Mean - The mean of sample is calculated by taking the sum of all data values and dividing by the total number of data values.
Melanin - A pigment that is found in plants, animals and protista. It is responsible for skin and hair pigmentation.
Melting Temperature T_m - The temperature at which one-half of a particular DNA duplex will dissociate and become single strand DNA.
Minisatellite Variant Repeat (MVR) - The temperature at which one-half of a particular DNA duplex will dissociate and become single strand DNA.
Mitochondrial DNA (mtDNA) - The genetic material found in mitochondria, the organelles that generate energy for the cell. Not inherited in the same fashion as nucleic DNA.
Mutation - When DNA damaged or changed anywhere along the DNA strand.

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

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Off Ladder (OL) Alleles - Alleles that size outside allele categories represented in the ladder.
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.
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.

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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.
Phenol - A chemical used in organic extraction. Polysaccharides and proteins are soluble in phenol, allowing for their separation from DNA. C₆H₅OH. See figure to the right.
Phenotype - The detectable outward manifestations of a specific genotype; the physical characteristics of a living object.
Polymerase Chain Reaction (PCR) - A technique for enzymatically replicating DNA without using a living organism.
Polymorphism - Variations in DNA sequences in a population that are detected in human DNA identification testing.
Polypurine - A stretch of adenine and/or guanine.
Polypyrimidine - A stretch of cytosine and/or thyamine.
Popstats - 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.
Preferential Amplification - Imbalanced amplification or lack of amplification at a locus.
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 - A quantitative description of the likely occurrence of a particular event, conventionally expressed on a scale of 0 to 1.
Probe - Defined nucleic acid (DNA or RNA) that can be used to identify, usually through autoradiography, specific DNA or RNA molecules bearing the complementary sequence.
Probability of Paternity - A formula that tests the hypothesis that the accused is the biological father of the child.
Product Rule - The probability of two independent events occurring simultaneously is the product of the individual probabilities. The rule stating that the probability of the occurrence of independent events is the product of their separate probabilities.
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.

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Quality Assurance Standards (QAS) - Quality assurance standards (for forensic DNA testing laboratories) written by the DNA Advisory board (established by the DNA Identification Act of 1994) and issued by the Director of the Federal Bureau of Investigation.
Quatitative 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.

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Racial Group - A group of people defined by race, color, nationality and ethnic or national origins.
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.
Reference Sample - 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).
Relative fluorescence unit (RFU) - 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).
Restriction Enzyme - An endonuclease that will recognize a specific target nucleotide sequence in DNA and break the DNA chain at the target.
Restriction Fragment Length Polymorphism (RFLP) - Restriction Fragment Length Polymorphism. A process used in DNA identification testing in which size (fragment length) differences at specific regions of the DNA are detected.

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Sanger Sequencing - A widely used method of determining the order of bases in DNA.
Sarkosyl - Also known as sodium lauroylsarcosine. A detergent used in DNA extraction.
Serology - The detection, identification, and typing of body tissues, either in native form or as stains or residues left at a crime scene.
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.
Serum - The liquid component of clotted blood. Serum lacks the formed elements and the clotting factors (which plasma includes), but retains the electrolytes and soluble proteins, including antibodies.
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.
Short Tandem Repeats (STR) - Multiple copies of a short identical DNA sequence arranged in direct succession in particular regions of chromosomes.
Sodium Dodecyl Sulfate (SDS) - Also known as sodium lauryl sulfate (SLS). A detergent used in DNA extraction.
Signal to Noise Ratio - A measure of signal strength relative to background noise.
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.
Single Nucleotide Polymorphism (SNP) - DNA sequence variations that occur when a single nucleotide (A, T, C, or G) in the genome sequence is altered.
Size Standard - See internal size standard
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.
spectrophotometry - The determination of the structure or quantity of substances by measuring their capacity to absorb light of various wavelengths.
Spermine - Polyamines originally isolated from semen and can inhibit PCR. Found in ribosomes and living tissues.
Spermidine - Polyamines originally isolated from semen and can inhibit PCR. Found in ribosomes and living tissues.
Supernatant - Liquid portion remaining after centrifugation or precipitation of a sample.

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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.
Thermal Cycler - An instrument used to perform the polymerase chain reaction (PCR).
Threshold - The point that must be exceeded to begin producing a given effect or result or to elicit a response.
Tris - An abbreviation for tris (hydroxymethyl)methylamine, also known as tris(hydroxymethyl)aminomethane. It is widely used in biochemistry as a buffer salt.

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No terms in this section

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Variance - A measure of the spread of a distribution about its average value.
Variable Number Tandem Repeat (VNTR) - A variable number tandem repeats (VNTR) is a short nucleotide sequences ranging from 14 to 100 nucleotides long that is organized into clusters of tandem repeats, usually repeated in the range of between 4 and 40 times per occurrence. Clusters of such repeats are scattered on many chromosomes.

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