Mitochondrial DNA, or mtDNA, is a type of genetic material found in the mitochondria, the energy-producing structures within cells. Unlike nuclear DNA, which is inherited from both parents, mtDNA is passed down exclusively from the mother. This unique inheritance pattern makes it useful for tracing maternal lineage and studying evolutionary relationships among species. mtDNA is relatively small compared to nuclear DNA and contains genes essential for the mitochondria's function, particularly in energy production. Mutations in mtDNA can lead to various mitochondrial diseases, affecting energy metabolism and overall health. Researchers study mtDNA to understand these conditions and explore human ancestry.