deoxyribonucleic acid mitochondrial DNA Typically small, circular, intronless, and maternally inherited, mitochondrial DNA (mtDNA) is the multicopy deoxyribonucleic acid genome of mitochondria, intracellular organelles responsible for vital respiratory chain and oxidative phosphorylation reactions in higher eukaryotes. Replicated and transcribed by a separate enzymatic machinery from that of nuclear DNA, mtDNA encodes only a subset of mitochondrial functions. (by EFO) http://www.ebi.ac.uk/efo/EFO_0008480 mtDNA