Mitochondrial DNA is the small circular chromosome found inside mitochondria. These organelles found in cells have often been called the powerhouse of the cell.[1] The mitochondria, and thus mitochondrial DNA, are passed almost exclusively from mother to offspring through the egg cell.
Electron microscopy reveals mitochondrial DNA in discrete foci. Bars: 200 nm. (A) Cytoplasmic section after immunogold labelling with anti-DNA; gold particles marking mtDNA are found near the mitochondrial membrane (black dots in upper right). (B) Whole mount view of cytoplasm after extraction with CSK buffer and immunogold labelling with anti-DNA; mtDNA (marked by gold particles) resists extraction. From Iborra et al., 2004.[2]

Mitochondrial DNA (mtDNA or mDNA)[3] is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, adenosine triphosphate (ATP). Mitochondrial DNA is only a small portion of the DNA in a eukaryotic cell; most of the DNA can be found in the cell nucleus and, in plants and algae, also in plastids such as chloroplasts.

Human mitochondrial DNA was the first significant part of the human genome to be sequenced.[4] This sequencing revealed that the human mtDNA includes 16,569 base pairs and encodes 13 proteins.

Since animal mtDNA evolves faster than nuclear genetic markers,[5][6][7] it represents a mainstay of phylogenetics and evolutionary biology. It also permits an examination of the relatedness of populations, and so has become important in anthropology and biogeography.