Glossary

In some cases several term explanations from different sources are included in parallel

References

Some terms included here are derived from sources available in the World Wide Web:

1. The Online Biology Dictionary
   http://www.biology-online.org/dictionary.asp
2. See-Kiong Ng: Automating Computational Molecular Genetics: Solving the Microsatellite Genotyping Problem, CMU-CS-98-105, School of Computer Science, Carnegie Mellon University, Pittsburgh, PA 15213
   http://reports-archive.adm.cs.cmu.edu/anon/1998/CMU-CS-98-105.pdf

A
Alleles	Alternative forms of a gene or marker. Alleles are inherited separately for each parent, as the chromosomes from the sperm and the egg pair up in reproduction.
Autosomes	Chromosomes that are not involved in sex determination. In human beings, each individual has two copies of each autosome (chromosomes 1 to 22), one inherited from each parent. See also sex chromosomes.
AVACH	German term for MEC (Allgemeine Vaterschaftsausschluss Chance), see MEC.
C
CA-repeats	A microsatellite marker containing tandem repeats of the simple DNA sequence CA (cytosine and adenine).
Centimorgan (cM)	A unit measuring recombination distance. A recombination distance of 1 cM is equal to a 1% chance that a marker at one genetic location will be separated from a marker at another location due to meiotic recombination (crossing over). In humans, 1 cM is roughly equal to 1 Mb (one million base pairs).
cM	See centimorgan.
Crossing over	A process occurring during meiosis in which two corresponding chromosome might exchange DNA (usually of the same locus or loci) before each member of the chromosome pair is incorporated into a sperm cell, respectively into an egg cell or a polar body. This process results in gene reshuffling; the further apart two genes are, the more likely it is for them to be reshuffled. This reshuffling likelihood (‘recombination likelihood’) is in turn used as a measure of how far apart two genes are, and is termed recombination distance. Its unit is centimorgan.
Crossing over	A process occurring during meiosis in which two corresponding chromosome might exchange DNA (usually of the same locus or loci) before each member of the chromosome pair is incorporated into a sperm cell, respectively into an egg cell or a polar body. This process results in gene reshuffling; the further apart two genes are, the more likely it is for them to be reshuffled. This reshuffling likelihood (‘recombination likelihood’) is in turn used as a measure of how far apart two genes are, and is termed recombination distance. Its unit is centimorgan.
D
Duo cases	Cases of disputed paternity consisting of a child and a putative father. (motherless cases). In ChrX testing, these cases are only resolvable for father/daughter constellations, which equals a mother/son constellations in skeletal identification cases.
DXS markers	D segs are chromosome-specific IDs that are useful for queries such as “d7s*” to find all markers on chromosome 7. D segs are commonly used to describe forensic markers with names such as dxs101 (a marker on the X chromosome)
E
Electrophoresis	A method used to separate mixtures of large molecules (e.g. DNA). A medium (e.g. a gel) containing the mixture is exposed to an electric field. Different molecules travel at different rates, depending on their electrical charges and sizes. See also gel electrophoresis.
EST	See expressed sequence tag.
Expressed sequence tag (EST)	A content-addressable label that is a subsequence of an expressed gene (cDNA).
Exon	The sequences of the primary RNA transcript (or the DNA that encodes them) that exit the nucleus as part of a messenger RNA molecule. In the primary transcript neighbouring exons are separated by introns.
G
Gene	The fundamental unit of heredity. A gene is a stretch of DNA that encodes a specific biological function or functional product (e.g. a polypeptide).
Gene localisation	Determination of the physical position of a gene on a chromosome.
Genetic markers	See markers
Genome	The genetic material of one particular organism.
Genotype	The genetic makeup of an individual in comparison to its actual physical and metabolic characteristics, which is called phenotype; the genotype of an human individual comprises two alleles per gene or marker; genes on the sex chromosomes are a special case.
Genotyping	Determination of which pair of alleles is present in an individual.
H
Haploid	Describes a nucleus, cell or organism possessing a single set of unpaired chromosomes. Gametes are haploid.
Haplotype	The set, made up of one allele of each gene, comprising the genotype. Also used to refer to the set of alleles on one chromosome or a part of a chromosome that tend to be inherited together, i.e. one set of alleles of linked genes. Its main current usage is in connection with the linked genes of the major histocompatibility complex.
Hemizygous	A situation within a cell where only one copy of a gene or group of genes is present instead of the usual two copies per gene in a diploid genome, e.g. the genes of the X and Y chromosomes in human males.
Hemizygosity	The state of being hemizygous.
Haplotyping	Setting the haplotype for a given individual.
Heterozygosity	The presence of different alleles at one or more loci on homologous chromosomes. Probability that an individual is heterozygous for any two alleles at a gene locus. Mathematically, where pi is the population frequency of the ith allele. See also polymorphic information content.
Heterozygous	An individual is heterozygous at a gene locus if the two alleles in the genotype are different. See also homozygous.
Homozygous	An individual is homozygous at a gene locus if the two alleles in the genotype are the same. See also heterozygous.
Hybridization	The binding of single strands of DNA or RNA to form double-stranded molecules.
I
Introns	Non-coding, intervening sequences of DNA that are transcribed, but are removed from within the primary gene transcript and rapidly degraded during maturation of messenger RNA. Most genes in the nuclei of eukaryotes contain introns, as do mitochondrial and chloroplast genes.
L
Linkage	The proximity between genes or markers along a chromosome. The closer the markers are, the less likely they are to be separated due to crossing over, hence it is the more likely that they will be inherited together. Also: The tendency for two or more genes to be inherited together, because they are located more or less closely on the same chromosome.
Linkage analysis	A method to map genes on a chromosome by evaluation the linkage of special markers (see Linkage Map). Today linkage analysis serves as a way of gene-hunting and genetic testing.
Linkage disequilibrium	The occurrence of some alleles together, more often than would be expected. In other words: The alleles are not inherited completely independent from one another.
Linkage equilibrium	Situation that should exist in an ideal population (a population undisturbed by selection, migration, etc.), in which all possible combinations of linked genes should be present at equal frequency. The situation is no more common than are such undisturbed populations.
Linkage group	A set of two or more loci that have been shown to be physically close on one chromosome and that are inherited together.
Linkage map	A map of the relative positions of genetic loci on a chromosome, determined onthe basis of how often the loci are inherited together. The distance is measured in centimorgans (cM). A map of the relative position of the markers and genes on a chromosome, determined by measuring how often the loci are inherited together. The unit of such a map is centimorgan (cM). See also physical map.
Locus	A location on a chromosome that can be identified in a distinctive manner. It might be occupied by a gene.
M
Marker	An identifiable location on a chromosome that expresses some measurable form of polymorphism so that its inheritance can be traced in a pedigree. It can be a gene itself or some segment of DNA with no known function (e.g. an STR).
MEC	Mean exclusion chance. MEC describes the power of markers for the exclusion of non biological father's.
MECKrüger	For autosomal markers in trio cases (mothe/child/putative father) after Krüger
MECKishida	For ChrX markers in trio cases (mother/daughter/putative father) after Kishida
MECDesmarais	For ChrX markers in trio cases (mother/ daughter/ putative father) after Desmarais: (synonym: PE = Power of exclusion)
MECDesmarais Duo	For ChrX markers in duo cases (daughter/putative father) after Desmarais (synonym: PE = Power of exclusion)
Meiotic recombinations	Recombination events caused by crossing over during meiosis.
Mutation	A permanent transmissible change in the genetic material, usually in a single gene. Also, an individual exhibiting such a change. Origin: Latin. Mutatio from mutare = to change
Mutation rate	The frequency with which a particular mutation appears in a population or the frequency with which any mutation appears in the whole genome of a population. Normally the precise use is implied by the context.
Mutation rate (in the context of this page)	Number of mutations / number of meiosis observed.
Microsatellites	Genetic markers that contain tandem repeats of short simple DNA sequences.
P
PCR	See polymerase chain reaction.
PCR stutter	Additional trailing shadow bands that occur during gel electrophoresis of PCR-amplified microsatellites. These bands are caused by the PCR products generated by polymerase slippage during PCR amplification.
Phase	The combined genotypes of two or more polymorphic loci on the same parental chromosome.
Phenotype	The observable features of an organism that results from the genotype.
Physical map	A map of the actual location of genes and markers on a chromosome measured in base pairs. See also linkage map.
PIC	See polymorphic information content.
Polymerase chain reaction (PCR)	A method to rapidly amplify a DNA fragment by alternatively denaturing double-stranded DNA, annealing pairs of primers to both ends of the DNA segment, and synthesizing the DNA bracketed by the primers using a heat-stable polymerase.
Polymorphic information content (PIC)	Probability that the marker genotype of a given offspring can be haplotyped. Mathematically, where pi and pj are the population frequencies of the ith and jth alleles. See also heterozygosity.
Polymorphism	Genetic variations in the DNA sequence of a gene or marker. A highly polymorphic gene or marker has a large number of possible alleles.
Primer	Short polynucleotide chain to which new deoxyribonucleotides can be added by DNA. A basic component required to perform a PCR.
R
Recombination	The process by which an offspring receives a combination of genes different from that of either parent. See also meiotic recombination. Occurring during meiosis, recombination is the re-arrangement of genes that results in a new combination of chromosomes that is capable of creating a unique gamete.
S
Sequence tagged site (STS)	A short DNA sequence (200 to 500 base pairs) with known location and base sequence that has a single occurrence in the genome. The STSs are used as unique landmarks when developing physical maps.
Sex chromosomes	The X and Y chromosomes in human beings that determine the sex of an individual. Females have two X chromosomes; males have an X and a Y-chromosome. See also autosomes.
STS	See sequence tagged site.
T
Tandem repeats	Multiple copies of the same nucleotide sequence on a chromosome situated one after the other, useful as markers in genetic analysis.
Tetranucleotid repeats	A microsatellite marker that contains tandem repeats of the simple DNA sequence consisting of 4-nucleotide-DNA-sequences (i.e. GATA, CTCA, AAAG etc).
Trio cases	Cases of disputed paternity consisting of mother/child/putative father)