Mitochondria are vital organelles found in all eukaryotic cells and convert chemical energy from food into ATP. The sequencing of mitochondrial DNA was the first important part of Human Genome Project (mtDNA is double stranded circular DNA about 16569 base pairs long). Mammalian mitochondrial DNA (mtDNA) is solely inherited from the mother. The mitochondria of the sperm vanish in embryogenesis in early stages by selective destruction, deactivation or by dilution by the superabundance of oocyte mitochondria. Pedigree illustrations of the genes of mitochondria reveal a mother passing trait to all her offsprings while father cannot pass the trait.
Mitochondrial DNA has several unique characteristics in comparison to nuclear DNA. The mutation rate in mitochondrial DNA is higher than the nuclear DNA as mitochondria is the site of oxidative phosphorylation where oxygen "free radicals" are released which damage DNA and, unlike nuclear DNA, mtDNA does not have any DNA repair enzymes. Also, the phenomenon of crossing over does not take place in mtDNA. Another contrast between two is that unlike nuclear DNA, mtDNA is not wrapped with histones and the genes are not characterised by interrupting DNA segments called 'introns' that do not code for proteins. Each mitochondrion has numerous copies of its DNA with different alleles for the same gene that can be present same cell. Among the thirty-seven genes that are present in mitochondria, twenty-four of them code for RNA molecules and thirteen other code for the proteins that have a role in cellular respiration.
Heteroplasmy is a state in which a specific mutation may be present in some mitochondrial DNA but not in others. After each cell division, the random distributions of mitochondria into daughter cells takes place and over time the mitochondrial chromosome tend to be all mutant type or all wild type for a particular gene. In the inheritance of mitochondrial mutations, only egg cells furnish mitochondria to the offspring therefore mitochondrial mutations display maternal inheritance. All of the mitochondria a mother passes to her children will be homoplasmic for a mutation if the mother is homoplasmic for that particular mtDNA mutation. And if the mother is heteroplasmic for that mtDNA mutation, then the possibility of her passing on the mutation to her children is decreased due to the chance distribution of both mtDNA and mitochondria during cell division. Therefore, the increased proportion of mutant mtDNA in the mother will result in increased chance of passing the mutation to her offsprings and therefore higher chance for the child to inherit the mutation.
Mitrochondrial DNA is very beneficial tool in forensic science. Although DNA based techniques such as polymerase chain reaction, short tandem repeat analysis and restriction fragment length polymorphism have been used in crime analysis, mtDNA is helpful in evaluating deteriorated samples or samples with scarcity of nuclear DNA. The mitochondrial genome is increasingly polymorphic, rendering it helpful for identification of humans. The 2 extremely variable regions HV1 and HV2 are generally amplified and analysis of sequence is carried out to compare the distinguishing features between the evidence and reference samples.
In the recent years the technique of mtDNA analysis is used to find victims of cold cases, bulk disasters like tsunami and earthquakes, to solve the cases of dead war soldiers and cases with confined biological material. Another instance of mtDNA is that it can be extracted from samples like hair shafts bones and tooth. mtDNA is present in high copy number, and is highly useful when there is little amount of sample to test.
Mitochondrial Dna is inherited solely from the mother it can be utilized to prove material linage, therefore mtDna analysis serves as a useful means of finding missing persons. the mtDNA from unrecognised remains can be compared with the mtDNA profile of maternal relative such as mother, sister, brother and her daughter, if the mtDNA profiles of the two individuals show similarities then they are related to each other. Maternal Lineage tests are devised from (mtDNA) which is transferred from a mother to her male and female offsprings. Thus mtDNA is a potent investigative means for researching the maternal line and maternal ancient ancestry. The 2 most famous applications of mtDNA testing is to disclose common maternal line ancestry and to discover one's ancient ancestral origins. Matrilineal most recent common ancestor popularly known as mitochondrial eve refers to not long past women from whom all present living humans descended that is counterpart of Y- chromosomal adam.
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