Mitochondrial DNA
Mitochondrial DNA was discovered in the 1960s by Margit M. K. Nass and Sylvan Nass by electron microscopy as DNase-sensitive threads inside mitochondria, and by Ellen Haslbrunner, Hans Tuppy and Gottfried Schatz by biochemical assays on highly purified mitochondrial fractions.
Human mitochondrial DNA haplogroup
The rate at which mitochondrial DNA mutates is known as the mitochondrial molecular clock. It's an area of ongoing research with one study reporting one mutation per 8000 years.