Mitochondrial DNAMitochondrial DNA (mtDNA) is DNA which is not located in the nucleus of the cell but in the mitochondria. Mitochondria are parts of the cell that generate fuel in the form of adenosine triphosphate (ATP), which drives the varied machinery of the cell.
Unlike most of the cell, the function of which is defined by the nuclear DNA, the mitochondria have their own DNA and are assumed to have evolved separately. Mitochondrial DNA consists of 5-10 rings of DNA and appears to carry 16,500 base pairs with 37 genes (13 proteins, 22tRNAs and two rRNA) which are concerned with the production of proteins involved in respiration. However they all need sub-units created by nuclear DNA in order to work.
mtDNA is typically passed on only from the mother during sexual reproduction (mitochondrial genetics), meaning that the mitochondria are clones. This means that there is little change in the mtDNA from generation to generation, unlike nuclear DNA which changes by 50% each generation. Since the mutation rate is easily measured, mtDNA is a powerful tool for tracking family lineage, and has been used in this role for tracking many species back thousands of generations.