| Carboxy- tetramethylrho- damine (TMR) |
A fluorescent molecule which,
after absorbing light, excites an electron at 546nm to a higher, unstable energy level and
emits fluorescent light at 572nm as the electron falls back to the lower energy level. |
| Carboxy-X- tetramethylrho- damine (CXR) |
A fluorescent molecule which,
after absorbing light, excites an electron at 580nm to a higher, unstable energy level and
emits fluorescent light at 605nm as the electron falls back to the lower energy level. |
| Chemiluminescence |
The generation of light as a
result of a chemical reaction. |
| CODIS "Combined DNA Index System" |
A national criminal database
that contains DNA profiles of individuals convicted of certain crimes. |
| Contamination |
The presence of foreign
substances (e.g., dirt or foreign DNA) in a DNA sample or testing reagent which
complicates or prevents correct interpretation of DNA typing results. |
|
|
D /Genetic Identity Glossary |
| DNA Database |
A repository of DNA
"fingerprints" maintained centrally for easy retrieval, the purpose of which is
to facilitate comparison of a known source of DNA with an unknown source of DNA. For
example, DNA evidence found at a crime scene or an unidentified body. See CODIS. |
| DNA Extraction |
The process whereby DNA is
purified from cells. |
| Doublet Bands |
Complementary strands of an
amplification product which vary in migration rates and are usually observed when using
post-staining detection. |
|
|
E /Genetic Identity Glossary |
| Electrophoresis |
The process of separating
charged molecules through a gel matrix by the application of an electric field. The gel
matrix has a sieving effect which allows molecules to be separated on the basis of size,
while the electric field separates molecules on the basis of charge. |
| Emission |
The condition in which an
electron falls back to a previous lower energy level and, in doing so, emits light of a
longer wavelength than the excitation light. |
| Excitation |
The condition in which an
electron moves to a higher, unstable energy level upon absorbing light. |
| Exclusion |
Positive elimination of an
individual suspected of being a criminal or father by virtue of a non-matching DNA
profile. |
|
|
F /Genetic Identity Glossary |
| Fluorescein |
A fluorescent molecule which,
after absorbing light, excites an electron at 490nm to a higher, unstable energy level and
emits fluorescent light at 520nm as the electron falls back to the lower energy level. |
| Fluorescent Dye |
Dye that consists of molecules
that selectively absorb light in the visible range or spectrum. The dye is fluorescent
because upon absorbing light, it instantly emits light at a longer wavelength than the
light absorbed. Examples of fluorescent dyes include fluorescein, tetramethylrhodamine and
carboxy-x-rhodamine. |
|
|
G /Genetic Identity Glossary |
| Genetic Identity |
The characterization of an
individual's genome by developing a unique DNA band (allele) pattern. |
| Genome |
The entire collection of
genetic information (contained in chromosomal DNA or RNA) in an organism. |
| Genotype |
The specific genes (which may
or may not be expressed) that are present in an organism. |
| Genotype Frequency |
The frequency with which a
specific allelic combination (genotype) occurs within a given population. |
|
|
H /Genetic Identity Glossary |
| Heteroduplex |
DNA composed of one wild-type
strand and a complementary strand with altered nucleotide sequence. |
| Heterozygous |
The presence of two different
alleles in an individual for a single genetic locus. |
| Homoduplex |
DNA composed of two strands
which are complementary in sequence (see Heteroduplex).
|
| Homozygous |
The presence of two identical
alleles in an individual for a single genetic locus. |
| Hybridization |
The annealing of two
complementary strands of nucleic acid to form a duplex molecule. |
| Hypervariable Region (HVR) |
A chromosomal segment
characterized by multiple alleles within a population for a single genetic locus. |
|
|
I /Genetic Identity Glossary |
| Inclusion |
The suggestive association of
identity between two DNA samples by virtue of a matching DNA profile. |
| Independent Assortment |
The random distribution of
whole chromosomes to the cell poles during anaphase assortment resulting in random
segregation of genes into daughter cells. In cases of independent assortment, the
segregation of one pair of alleles does not alter the segregation of another pair of
alleles. |
|
|
L /Genetic Identity Glossary |
| Labeling |
A process in which nucleic
acids are tagged with a radioactive or non-radioactive marker. |
| Laser |
A device that converts incident
electromagnetic radiation of mixed frequencies to one or more discrete frequencies of
highly amplified ultraviolet, visible or infrared radiation. |
| Locus |
The position of a gene or
chromosome segment on a chromosome. Alleles are located at identical loci on homologous
chromosomes. |
| Luminograph |
A photographic record of a
luminescent event. |
|
|
M /Genetic Identity Glossary |
| Matching Probability |
The average number of people
one would have to survey before finding the same DNA pattern as a randomly selected
individual. Sometimes called the Power
of Discrimination. |
| Microheterogeneity |
A length variation that is
smaller than one locus-specific repeat length. See microvariants. |
| Microvariants |
Alleles differing from one
another by lengths shorter than the repeat length. |
| Minisatellite |
Regions of DNA consisting of
tandemly repeated short sequences of DNA. |
| Mismatch |
Occurs when short
oligonucleotide probes or primers bind to single-stranded sample DNA that is not
completely complementary. See stringency. |
| Modifying Enzymes |
A group of enzymes used to
synthesize, degrade, join or remove portions of nucleic acids in a controlled and
generally defined manner. |
| Multi-Locus Probe |
A probe that hybridizes to
several loci. |
| Multiplex |
A combination of two or more
STR loci during both amplification and analysis. All multiplex STR loci are amplified
simultaneously in a single tube. Also, because each STR locus has a limited size range of
known alleles, several STR loci are detected simultaneously in limited and well-defined
regions of the same lane on a gel. |
| Mutation |
Any detectable and heritable
change (base deletions, insertions or substitutions) in a DNA sequence. |
|
N /Genetic Identity Glossary |
| N-4 Band |
See Stutter Band. |
|
O /Genetic Identity Glossary |
| Oligonucleotide |
A polymer of DNA or RNA
nucleotides (typically <50 nucleotides) that is usually synthesized by an automated
system, and is generally used as a probe or primer. |
|
P /Genetic Identity Glossary |
| Paternity Index |
How many times more likely it
is that the man being tested is the father, rather than a randomly selected individual. |
| Polymerase Chain Reaction (PCR) |
A repetitive process, usually
aided by the action of a thermostable (heat-stable) DNA polymerase, which copies a DNA
template such that the number of copies increases exponentially. A typical procedure
involves cycles of template denaturation, primer annealing and extension. |
| Polymorphism |
The simultaneous occurrence of
two or more allelic forms within the population. |
| Population |
A collection of individuals
having specific features (common alleles of polymorphic loci) present in Hardy-Weinberg
equilibrium. |
| Power of Discrimination |
The average number of people
one would have to survey before finding the same DNA pattern as a randomly selected
individual. Sometimes called Matching
Probability. |
| Power of Exclusion |
The fraction of individuals who
would not have the DNA pattern presented in a typical paternity case. |
| Primer |
An oligonucleotide or short
single-stranded nucleic acid which, upon hybridization with a complementary portion of
another single-stranded molecule, acts as a starting point for initiation of
polymerization mediated by an enzyme with DNA polymerase activity. |
| Probe |
A labeled single-stranded
fragment of DNA or RNA which can be hybridized to a complementary target sequence. |
| Purification |
The process by which DNA is
extracted from cells and separated from other nuclear and cellular material. |
|
Q /Genetic Identity Glossary |
| Quality Control |
A set of product specifications
which prioritizes and links the product development process so that it assures high
quality as defined by the end-user. |
|
R /Genetic Identity Glossary |
| Real-time Analysis |
Electrophoretic gels are
scanned by the fluorescent scanning instrumentation as they are running. This on-line
analysis requires more instrumentation to achieve the same throughput as batch anaylsis. |
| Repeat Slippage |
Artifact produced due to the
loss of a repeat unit during DNA synthesis through regions of repeated sequence. Also
referred to as "stuttering", "shadow banding" or "n-4". |
| Restriction Endonuclease |
An enzyme that recognizes a
specific short base sequence of DNA and cleaves both DNA strands, either within the
recognition site or at a defined distance from it. |
| Restriction Fragment Length Polymorphism (RFLP) |
A DNA polymorphism which is
detected as different fragment lengths following digestion with a specific restriction
endonuclease. |
| Restriction Site |
The specific DNA sequence to
which a restriction enzyme binds. Also called recognition site or recognition sequence. |
|
S /Genetic Identity Glossary |
| Shadow Band |
Artifact produced due to the
loss of a repeat unit during DNA synthesis through regions of repeated sequence. Also
referred to as "repeat slippage",
"stuttering" or "n-4". |
| Short Tandem Repeat (STR) |
Different numbers of tandemly
repeated core DNA sequences, 3 to 7 base pairs in length, at a given locus. |
| Single-locus Probe |
A probe that hybridizes to a
single locus. |
| Size Marker |
A DNA standard of known size
which can be used to estimate the sizes of unknown DNA in an electrophoretic gel. |
| Southern Blot |
The technique whereby DNA
fragments separated by agarose gel electrophoresis are transferred to a membrane (usually
nylon). These fragments are generally detected by hybridization with labeled complementary
probes. |
| Stringency |
The degree to which either base
pair mismatches or completely complementary strands of DNA are allowed to hybridize.
Stringency is controlled by temperature, buffer salt concentration and probe length. |
| Stutter Band |
Artifact produced due to the
loss of a repeat unit during DNA synthesis through regions of repeated sequence. Also
referred to as "repeat slippage",
"shadow banding" or
"n-4". |
| Subpopulation |
Individuals within a given
population that are further defined by some recognizable level of relatedness. |
|
T /Genetic Identity Glossary |
| Tandem Repeat |
The repeated end-to-end
duplication of a core DNA sequence at a defined locus. |
| Thermal Cycler |
Instrument capable of
generating and maintaining specific temperatures for defined periods of time. Thermal
cyclers are used for PCR amplification. |
| Thermostable DNA Polymerase |
DNA polymerase enzymes that are
resistant to heat and retain their function after exposure to tempratures up to
95°C. |
| TMR |
Carboxy-tetramethylrhodamine |
|
V /Genetic Identity Glossary |
| Validation Study |
Rigorous testing of a new DNA
identification system or methodology to determine reliability and other performance
characteristics before it is used in actual forensic or paternity applications. |
| Variable Number of Tandem Repeats (VNTR) |
Different numbers of tandemly
repeated core DNA sequences at a given locus. |
|
