WHAT IS DNA?
Deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or (MtDNA)
DNA is essentially the molecule that holds all genetic information and ‘instructions’ for an organism. The human genome is composed of over 3 billion base pairs of information organised into 23 chromosomes. Genes are the regions of DNA that encode and regulate protein synthesis, though this involves just 1.5% of the entire genome. A significant amount of the human genome, approximately 75%, consists of extragenic DNA, which contains regions that do not actually contain known gene sequences. About 50% of extragenic DNA is made up of something called repetitive DNA, which is of particular use in forensic DNA analysis. Repetitive DNA is further sub-divided into tandem repeats (including satellite DNA, microsatellites and minisatellites) and interspersed repeats (SINE, LINE, LTR and Transposon). Tandem repeat DNA and the variation between them (polymorphisms) is the focus of many DNA profiling techniques. It is due to the number and location of these polymorphisms that every individual has unique DNA which produces a distinctive band pattern when analysed.
DNA is essentially the molecule that holds all genetic information and ‘instructions’ for an organism. The human genome is composed of over 3 billion base pairs of information organised into 23 chromosomes. Genes are the regions of DNA that encode and regulate protein synthesis, though this involves just 1.5% of the entire genome. A significant amount of the human genome, approximately 75%, consists of extragenic DNA, which contains regions that do not actually contain known gene sequences. About 50% of extragenic DNA is made up of something called repetitive DNA, which is of particular use in forensic DNA analysis. Repetitive DNA is further sub-divided into tandem repeats (including satellite DNA, microsatellites and minisatellites) and interspersed repeats (SINE, LINE, LTR and Transposon). Tandem repeat DNA and the variation between them (polymorphisms) is the focus of many DNA profiling techniques. It is due to the number and location of these polymorphisms that every individual has unique DNA which produces a distinctive band pattern when analysed.
Sources of DNA
In terms of forensic DNA analysis, there is a variety of possible sources of DNA evidence. The more useful sources include blood, semen, vaginal fluid, nasal secretions and hair with roots. It is theoretically possible to obtain DNA from evidence such as urine, feces and dead skin cells, though this is often classed as a poor source due to the lack of intact cells and high levels of contaminants preventing successful analysis. Such samples will be collected depending on the type of sample.