Mitochondrial DNA (mtDNA)'s the DNA located in organelles called mitochondria. Most other DNA present in eukaryotic organisms's found in the cell nucleus. Mitochondrial DNA was discovered by Margit M. K. Nass and Sylvan Nass by electron microscopy as DNAase-sensitive thread inside mitochondria, and by Ellen Haslbrunner, Hans Tuppy and Gottfried Schatz by biochemical assays on highly purified mitochondrial fractions. Nuclear and mitochondrial DNA are thought to be of separate evolutionary origin… (More on Mt-dna)