Glossary
A
single-letter designation of the purine base adenine; also used in diagrams to represent a nucleotide containing adenine
Adenine
a purine base; one of the four nitrogen-containing molecules present in nucleic acids DNA and RNA; designated by the letter A
Allele
one of two or more alternative forms of a gene
Allele frequency
the proportion of a particular allele among the chromosomes carried by individuals in a population
AMP-FLP
amplified fragment length polymorphism
Autoradiogram (autoradiograph; autorad)
a photographic recording of the positions on a film where radioactive decay of isotopes has occurred
AutosomeY
any of the chromosomes other than the sex chromosomes, X and
Band
the visual image representing a particular DNA fragment on an autoradiogram
Band shift
the phenomenon in which DNA fragments in one lane of a gel migrate at a rate different from that of identical fragments in other lanes of the same gel
Basepair
two complementary nucleotides held together by hydrogen bonds; basepairing occurs between A and T and between G and C
Biallelic
(see Diallelic)
Blot
see Southern blot
C
single-letter designation of the pyrimidine base cytosine; also used in diagrams to represent a nucleotide containing cytosine
Chromosome
the structure by which hereditary information is physically transmitted from one generation to the next; the organelle that carries the genes
Controls
tests performed in parallel with experimental samples and designed to demonstrate that a procedure worked correctly
Cytosine
a pyrimidine base; one of the four nitrogen-containing molecules in nucleic acids DNA and RNA; designated by the letter C
Degradation
the breaking down of DNA by chemical or physical means
Denaturation
the process of unfolding of the complementary double strands of DNA to form single strands
Deoxyribonucleic acid (DNA)
the genetic material of organisms, usually double-stranded—composed of two complementary chains of nucleotides in the form of a double helix; a class of nucleic acids characterized by the presence of the sugar deoxyribose and the four bases adenine, cytosine, guanine, and thymine
Diallelic DNA
variation showing only two forms with a frequency of more than 1%
Diploid
having two sets of chromosomes, in pairs (compare haploid)
DNA
deoxyribonucleic acid
DNA band
the visual image representing a particular DNA fragment on an autoradiogram
DNA databank (database)
a collection of DNA typing profiles of selected or randomly chosen individuals
DNA polymerase
an enzyme that catalyzes the synthesis of double-stranded DNA
DNA probe
a short segment of single-stranded DNA labeled with a radioactive or chemical tag that is used to detect the presence of a particular DNA sequence through hybridization to its complementary sequence
Electrophoresis
a technique in which different molecules are separated by their rate of movement in an electric field
Enzyme
a protein that is capable of speeding up a specific chemical reaction but which itself is not changed or consumed in the process; a biological catalyst
Ethidium bromide
an organic molecule that binds to DNA and fluoresces under ultraviolet light and is used to identify DNA
G
single-letter designation of the purine base guanine; also used in diagrams to represent a nucleotide containing guanine
Gamete
a haploid reproductive cell
Gametic (phase) equilibrium
the state at loci on different chromosomes when the allele at one locus in the gamete varies independently of that at the other loci; in gametic (phase) disequilibrium, a specific allele at one locus is associated with an allele at another locus on a different chromosome with a frequency greater than expected by chance (see linkage disequilibrium)
Gel
semisolid matrix (usually agarose or acrylamide) used in electrophoresis to separate molecules
Gene
the basic unit of heredity; a sequence of DNA nucleotides on a chromosome
Gene frequency
the relative occurrence of a particular allele in a population
Genetic drift
random fluctuation in allele frequencies
Genome
the total genetic makeup of an organism
Genotype
the genetic makeup of an organism, as distinguished from its physical appearance or phenotype
Guanine
a purine base; one of the four nitrogen-containing molecules present in nucleic acids DNA and RNA; designated by the letter G
Haploid
having one set of chromosomes (compare diploid)
Hardy-Weinberg
equilibrium the condition, for a particular genetic locus and a particular population, with the following properties: allele frequencies at the locus are constant in the population over time and there is no statistical correlation between the two alleles possessed by individuals in the population; such a condition is approached in large randomly mating populations in the absence of selection, migration, and mutation
Heredity
the transmission of characteristics from parent to offspring
Heterozygote
a diploid organism that carries different alleles at one or more genetic loci on its homologous chromosomes
Heterozygous
having different alleles at a particular locus; for most forensic DNA probes, the autoradiogram displays two bands if the person is heterozygous at the locus
HLA
see human leukocyte antigen
Homology
similarity between two structures or functions indicative of a common evolutionary origin
Homozygote
a diploid organism that carries identical alleles at one or more genetic loci on its homologous chromosomes
Homozygous
having the same allele at a particular locus; for most forensic DNA probes, the autoradiogram displays a single band if the person is homozygous at the locus
Human leukocyte antigen (HLA)
protein-sugar structures on the surface of most cells, except blood cells, that differ among individuals and are
important for acceptance or rejection of tissue grafts or organ transplants; the locus of one particular class, HLA DQ, is used for forensic analysis with PCR
Hybridization
the reassociation of complementary strands of nucleic acids, nucleotides, or probes
Isotope
an alternative form of a chemical element; used particularly in reference to the radioactive alternative forms, or radioisotopes
Linkage
disequilibrium the phenomenon in which a specific allele at one locus is non-randomly associated with an allele at another locus
Locus (pl. loci)
the specific physical location of a gene on a chromosome
Marker
a gene with a known location on a chromosome and a clear-cut phenotype that is used as a point of reference in the mapping of other loci
Membrane
the matrix (usually nylon) to which DNA is transferred during the Southern blotting procedure
Molecular-weight size marker
DNA fragments of known size, from which the size of an unknown DNA sample can be determined
Monomorphic probe
a probe that detects the same allele and hence the same pattern in everyone
Multilocus probe
a DNA probe that detects genetic variation at multiple sites; an autoradiogram of a multilocus probe yields a complex, stripelike pattern of 30 or more bands per individual
Mutagen
a physical agent (e.g., x rays) or chemical agent that induces changes in DNA
Nucleic acid
a nucleotide polymer of which major types are DNA and RNA
Nucleotide
a unit of nucleic acid composed of phosphate, a five-carbon sugar (ribose or deoxyribose), and a purine or a pyrimidine base
PCR
polymerase chain reaction
Phenotype
the physical appearance or functional expression of a trait
Point mutation
an alteration of one nucleotide in chromosomal DNA that consists of addition, deletion, or substitution of nucleotides
Polymerase chain reaction (PCR)
an in vitro process that yields millions of copies of desired DNA through repeated cycling of a reaction that involves the enzyme DNA polymerase
Polymorphism
the presence of more than one allele of a gene in a population at a frequency greater than that of a newly arising mutation; opera-
tionally, a population in which the most common allele at a locus has a frequency of less than 99%
Population
a group of individuals occupying a given area at a given time
Probe
a short segment of single-stranded DNA tagged with a reporter molecule, such as radioactive phosphorus atom, that is used to detect a particular complementary DNA sequence
Proficiency tests
tests to evaluate the competence of technicians and the quality performance of a laboratory; in open tests, the technicians are aware that they are being tested, but in blind tests, they are not aware; internal proficiency tests are conducted by the laboratory itself, and external tests are conducted by an agency independent of the laboratory being tested
Protein
a chain of amino acids joined by peptide bonds
Purine
the larger of two kinds of bases found in DNA and RNA; a nitrogenous base with a double-ring structure, such as adenine or guanine (compare pyrimidine)
Pyrimidine
the smaller of two kinds of bases found in DNA and RNA; a nitrogenous base with a single-ring structure, such as cytosine, thymine, and uracil (compare purine)
Quality assurance
a program conducted by a laboratory to ensure accuracy and reliability of tests performed
Quality control
internal activities or activities according to externally established standards used to monitor the quality of DNA typing to meet and satisfy specified criteria
Recombinant DNA
fragments of DNA from two different species, such as a bacterium and a mammal, spliced into a single molecule
Replication
the synthesis of new DNA from existing DNA
Restriction endonuclease, restriction enzyme
an enzyme that cleaves DNA molecules at particular base sequences
Restriction fragment length polymorphism (RFLP)
variation in the length of DNA fragments produced by a restriction endonuclease that cuts at a polymorphic locus
RFLP
restriction fragment length polymorphism
RFLP analysis
technique that uses single-locus or multi-locus probes to detect variation in a DNA sequence according to differences in the length of fragments created by cutting DNA with a restriction enzyme
Ribonucleic acid (RNA)
a class of nucleic acids characterized by the presence of the sugar ribose and the pyrimidine uracil, as opposed to the thymine of DNA
RNA
ribonucleic acid
Serology
the discipline concerned with the immunologic study of body fluids
Serum
the liquid that separates from blood after coagulation
Sex chromosomes (x and y chromosomes)
chromosomes that are different in the two sexes and that are involved in sex determination
Sex-linked characteristic
a genetic characteristic, such as color blindness, that is determined by a gene on a sex chromosome and shows a different pattern of inheritance in males and females; X-linked is a more specific term
Single-locus probe
a DNA probe that detects genetic variation at only one site in the genome; an autoradiogram that uses one single-locus probe usually displays one band in homozygotes and two bands in heterozygotes
Somatic cells
the differentiated cells that make up the body tissues of multicellular plants and animals
Southern blot
the nylon membrane to which DNA adheres after the process of Southern blotting
Southern blotting
the technique for transferring DNA fragments that have been separated by electrophoresis from the gel to a nylon membrane
Standards
criteria established for quality control and quality assurance; established or known test reagents, such as molecular-weight standards
T
single-letter designation of the pyrimidine base thymine; also used in diagrams to represent a nucleotide containing thymine
Tandem repeats
multiple copies of an identical DNA sequence arranged in direct succession in a particular region of a chromosome
Taq polymerase
a DNA polymerase used to form double-stranded DNA from nucleotides and a single-stranded DNA template in the PCR technique
Thymine
a pyrimidine base; one of the four nitrogen-containing molecules present in nucleic acids DNA and RNA; designated by the letter T
Uracil
a pyrimidine in RNA
Variable number of tandem repeats (VNTR)
repeating units of a DNA sequence for which the number varies between individuals
VNTR
variable number of tandem repeats
Zygote
diploid cell that results from the fusion of male and female gametes