Mitochondrial DNA
in addition to nuclear DNA, humans (like almost all karyotes) have mitochondrial DNA
Mitochondria, the "power houses" of a cell, have their own DNA because they are descended from a proteobacterium that merged with eukaryotic cells over 2 billion years ago an assertion known as the endosymbiotic hypothesis.
Mitochondria are inherited from one's mother, and its DNA is frequently used to trace maternal lines of descent (see mitochondrial Eve).
Mitochondrial DNA is only 16 kb in length and encodes for 62 genes