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How is Mitochondrial DNA (mtDNA) Used in Forensics

written by: KM•edited by: Leigh A. Zaykoski•updated: 6/27/2011

Are you wondering how mitochondrial DNA is used in forensics? Read on for an introduction into this exciting branch of science.

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    Deoxyribonucleic Acid

    The deoxyribonucleic acid (DNA) contains all the information that enables the human body to function properly. In human cells, DNA can be found both in the nucleus which is referred to as the cell’s brain for it manages almost all vital process of the cell; the other DNA is in the mitochondria also known as the powerhouse because of its involvement in energy production. The nucleus has two copies of DNA, one parental and the other maternal both intricately woven into chromosomes. Some human cells may have as few as a single nucleus while, the number of mitochondria present in one cell can reach up to hundreds, all depending on the cell’s energy requirements; moreover, these mitochondrial DNA (mtDNA) can be copied up to ten times.

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    Nuclear DNA & mtDNA

    Nuclear DNA is relatively longer than mitochondrial DNA reaching up to 3 billion base pairs compared to the estimated 16,569 bases pairs of mtDNA. However, scientists in the early 1990s proposed the use of mtDNA and its applications have greatly improved because of its size, its large number of copies within a single cell, its numerous sequence variations and its hypervariable (greater number of polymorphism) region. This higher number of copy of mtDNA in a single cell makes it extremely useful for forensics experts to extract them and process them for mitochondrial DNA typing particularly in cases where there are limited resources and samples. In addition to this, there are kinds of biological materials that are often present in crime scenes such as teeth, bones and hair shafts that do not contain nucleus but posses mtDNA hence making identification possible.

    Aside from the number of mtDNA that can be extracted coming from small amount of samples, mitochondrial DNA proved very helpful in forensics because of its mode of inheritance. In humans, the mtDNA are strictly inherited from the mothers, therefore relatives that come from the same maternal lineage like brothers and sisters, mother and daughters will possess the same mtDNA, this will hold true in the complete absence of mutation. Because of this, relatives can directly supply mtDNA for forensic identification. However, this advantage of the mitochondrial DNA is, ironically its loophole. With the use of mtDNA in analysis, it will not be able to distinguish and even identify evidences and materials that do not come from the same maternal lineage which nuclear DNA analysis can easily provide given the right amount and kind of samples.

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    Location of mtDNA

    The location of the mtDNA as well compared to that of the nuclear DNA has been an advantage for using mtDNA in forensics analysis. This detail can be further shown in the case of identifying the victims of the Rwanda massacre where an estimated 500,000 corpses were dumped in mass graves. Due to the heat and the humidity of the place, nuclear DNA samples proved challenging to isolate and be processed, hence mtDNA played a major role in identifying the victims. The location and the ideal structure of mtDNA makes it difficult to degrade even when exposed to various environmental factors. These mtDNAs as well are protected by a substance called hydroxyapatite which are also found as covering for bones and teeth.