Mitochondrial DNA (mtDNA)

Mitochondrial DNA (mtDNA, or less common mDNA) is DNA that is found in Mitochondria. Mitochondria is the part of organic cells that produce most of the cellular energy by converting organic materials into Adenosine Triphosphate (ATP) via the process of oxidative phosphorylation. Typically nuclear DNA determines the function a cell, however mitochondria have their own DNA and are assumed to have evolved separately (Endosymbiotic theory).

Mitochondrial DNA (mtDNA) analysis is useful in forensic cases in which nuclear DNA is insufficient for short tandem repeat (STR) typing. Shed body, head, and pubic hairs with no cellular material (hair follicle) attached to the root bulb and aged skeletal remains are the samples most commonly analyzed for mtDNA because nuclear DNA is not recoverable from these tissues. Usually a cell has hundreds or thousands of mitochondria which can occupy up to 25% of the cell's cytoplasm, and each mitochondrion contains 1-10 mtDNA molecules. The high copy number of mtDNA molecules found in each cell is one reason why mtDNA is recoverable from hairs and old skeletal remains.

Mitochondria in the sperm from the father are typically destroyed by the female egg cell immediately after fertilization, leaving behind only mtDNA from the mother. In 1999 it was reported that paternal sperm mitochondria (containing mtDNA) are marked with ubiquitin to select them for later destruction inside the embryo (Sutovsky et. al. 1999). Therefore the mother's mtDNA is passed on to the next generation; the fathers is typically not. However, it has also been proven that about 1-2% of a person's mitochondria can be inherited from the father.

Comparison of Mitochondrial DNA to Nuclear DNA

Number of Copies - There are only 2 Nuclear DNA Molecules in each cell as opposed to 100's to 1000's of Mitochondrial DNA per cell.

Inheritance - mtDNA is typically passed on only from the mother during sexual reproduction (mitochondrial genetics), meaning that the mitochondria are clones. This means that there is little change in the mtDNA from generation to generation, unlike nuclear DNA which is inherited from both the Mother and Father and changes by 50% each generation.

Location - Both Nuclear DNA and mtDNA are located in all cells except red blood cells. Nuclear DNA is located in the nucleus of a cell, and mtDNA is located in the mitochondria of the cell.

Structure and Composition - Both Nuclear DNA and Mitochondrial DNA have a double helix structure composed of Adenine (A), Cytosine (C), Guanine (G), Thymine (T). Nuclear DNA are linear molecules composed of 46 chromosomes and 3 billion nucleotides. Mitochondrial DNA are circular molecules and only contain 16,569 nucleotides.