Mitochondrial DNA (mtDNA) is the DNA located in organelles called mitochondria, structures within cells that convert the energy from food into a form that cells can use. Most other DNA present in eukaryotic organisms is found in the cell nucleus. Nuclear and mitochondrial DNA are thought to be of separate evolutionary origin, with the mtDNA being derived from the circular genomes of the bacteria that were engulfed by the early ancestors of today's eukaryotic cells. Each mitochondrion is estima… (More on Mtdna)