Allele - any of several alternative forms of a gene or STR locus found at the same point on a particular pair of chromosomes.
ASCLD/LAB - the American Society of Crime Laboratory Directors / Laboratory Accreditation Board. An organisation that provides accreditation and quality testing for forensic laboratories around the world. ESR is accredited under ASCLD/LAB to perform forensic DNA analysis as well as several other forensic analyses.
Bayesian - a statistical method of combining the likelihood ratio with additional information to produce an overall estimate of the strength of a piece of evidence. Named after the Reverend Thomas Bayes (1702-1761).
Buccal sample/swab - a sample collected by rubbing a sterile swab on the inside of the mouth or cheek. This transfers loose skin cells onto the swab, cells which can then be used to generate a DNA profile.
Chromosome - a rod-shaped structure found inside most human cells. Consist mainly of long coils of DNA, and as such are the storage unit of DNA in the cell. Humans have 23 pairs of chromosomes; one set of 23 inherited from the father, the other set from the mother.
CI(BS) Act - the Criminal Investigations (Bodily Samples) Act 1995. This was originally passed in 1995 as the Criminal Investigations (Blood Samples) Act and was amended to its current form in 2003. The Act deals with regulations regarding samples for use on the National DNA Database.
CSDU/CSD - Crime Sample Database Unit. This is the team at ESR that works on samples from volume crimes that have no specific suspect, such as burglaries. DNA profiles produced by the CSDU are loaded onto the Crime Sample Database (CSD) and are matched against the profiles from individuals on the National DNA Database (NDD).
Defence Hypothesis - the defence hypothesis is assumes to be that the biological evidence seen in a case is not from the suspect, but from another unrelated person in the wider population. This assumption is used in the statistical calculations that evaluate a piece of evidence.
DNA - deoxyribonucleic acid. The molecule that carries genetic information and can be found in almost all living cells.
Electrophoresis - a technique that separates DNA fragments on the basis or their size by running them through a viscous material. The fragments move through the material due to the application of an electric current which attracts the negatively charged DNA to the positive terminal, and the fragments are separated due to the fact that the smaller fragments will move through the matrix faster than the larger fragments and will thus arrive sooner at the positive terminal.
Fst - a statistical term used to measure the level of inbreeding in a subpopulation. This has an effect on the distribution of the alleles seen in DNA profiles and is used by forensic scientists to calculate how rare a certain DNA profile is.
Gene - a section of DNA that contains the genetic information contained in the DNA of an organism.
Genome - the complete set of genetic information contained in the DNA of an organism.
Heterozygote - a person who has two different alleles, one on each chromosome, at a single locus.
Homozygote - a person who has two copies of the same allele, one on each chromosome, at a single locus.
LCN - Low Copy Number. Refers to a relatively new method of DNA analysis that uses increased PCR cycle numbers to detect extremely small amounts of DNA.
Likelihood Ratio - a statistical term that measures the value of a piece of evidence. Equal to the probability of seeing a piece of evidence given the prosecutor's hypothesis, divided by probability of seeing a piece of evidence given the defence hypothesis.
Locus - a specific area, or site, on a chromosome. DNA profiling looks at ten STR loci.
Mitochondrial DNA - a relatively new method of DNA analysis that examines the DNA in mitochondria, which are small organelles responsible for producing the energy in cells. Mitochondrial DNA techniques are not as discriminating as traditional methods, but because mitochondria are resistant to degradation, it can be very useful in identifying badly burnt or decomposed samples.
Multiplex - a form of DNA analysis that allows multiple loci to be analysed at the same time.
NDD - National DNA Database. A database of known DNA profiles maintained by ESR. There are around 64,000 individuals on the NDD. Profiles on the NDD are compared with those on the Crime Sample Database (CSD), which contains unknown DNA profiles from crime scenes.
Nucleotide - the base unit of DNA. Nucleotides make up the 'rungs' of the ladder-shaped DNA double helix. Nucleotides can be either A,G,C or T and different combinations of these are used to encode the information that DNA contains.
PCR Amplification - PCR stands for Polymerase Chain Reaction, and refers to a method for increasing small amounts of DNA into an amount that can be more easily analysed. This is achieved through a copying process that is repeated many times, doubling the number of DNA molecules present at each stage.
PCT - Priority Casework Team. The team at ESR that deals with DNA cases where a suspect has been identified. This often involves work on high profile cases such as homicides, rapes, etc.
Polymorphism - having multiple forms of an allele at a locus within a population. Forensic scientists look for areas of DNA that are polymorphic because these allow people to be told apart from each other by their DNA.
Prosecutor's Hypothesis - the prosecutor's hypothesis is assumed to be that the biological evidence seen in a case originated from the suspect. This assumption is used in statistical calculations that evaluate the value of a piece of evidence.
RFLP - Restriction Fragment Length Polymorphism. An old method of forensic DNA analysis based on the different sized fragments that can be produced when a piece of DNA is cut by certain enzymes. Replaced by STR analysis due to the large amount of DNA required for it to work, as well as the long time needed for analysis.
SGM Plus - the STR multiplex used by ESR to generate DNA profiles from biological samples. Contains ten different STR loci as well as the sex test Amelogenin.
STR - Short Tandem Repeat. The form of forensic DNA analysis currently used by most forensic laboratories around the world. STRs are short sequences of nucleotides that repeat themselves multiple times at certain points in the genome. Different people tend to have different numbers of the repeat unit in their DNA, and this allows people to be told apart on the basis of their DNA.
Trace DNA - extremely small amounts of DNA such as, for example, the few skin cells that may be left behind when a person touches something with their hands. In recent years it has become possible to obtain DNA profiles from trace levels of DNA.