Mitochondrial DNA (mtDNA) is a type of DNA located outside the nucleus in the liquid portion of the cell (cytoplasm) and inside cellular organelles called mitochondria. Mitochondria are found in all complex or eukaryotic cells, including plant, animal, fungi, and single celled protists, which contain their own mtDNA genome.
Margulis, Lynn, 1938-2011
Lynn Petra Alexander Sagan Margulis studied cells and mitochondria in the US during the second half of the twentieth century. She developed a theory for the origin of eukaryotic cells. In that theory, she proposed that two kinds of structures found in eukaryotic cells, mitochondria in animals and plastids in plants, were once free-living bacteria that lived harmoniously and in close proximity to larger cells, a scenario
All cells that have a nucleus, including plant, animal, fungal cells, and most single-celled protists, also have mitochondria. Mitochondria are particles called organelles found outside the nucleus in a cell's cytoplasm. The main function of mitochondria is to supply energy to the cell, and therefore to the organism.