Human mitochondrial DNA haplogroup

Mitochondria are the primary energy generator of the cell and have unique organelles that maintain their own DNA (mtDNA). In human genetics, human mitochondrial DNA haplogroups are collections of similar haplotypes defined by combinations of single nuclear polymorphism (SNPs) in mtDNA inherited from a common ancestor. Mitochondrial DNA is passed down through cytoplasmic inheritance, where, upon fertilization, the paternal mitochondria are degraded, leaving only the maternal mitochondria regardless of the offspring’s sex. This characteristic of mitochondrial inheritance allows geneticists to track the movement and divergence of different haplogroups from female lineages. Haplogroups are used to represent the major branch points on the mitochondrial phylogenetic tree. Understanding this mechanism of inheritance has helped population geneticists trace the matrilineal inheritance of modern humans back to human origins in Africa and the subsequent spread around the globe.

The letter names of the haplogroups (not just mitochondrial DNA haplogroups) run from A to Z. As haplogroups were named in the order of their discovery, the alphabetical ordering does not have any meaning in terms of actual genetic relationships.

The hypothetical woman at the root of all these groups (meaning just the mitochondrial DNA haplogroups) is the matrilineal most recent common ancestor (MRCA) for all currently living humans. She is commonly called Mitochondrial Eve.

The rate at which mitochondrial DNA mutates is known as the mitochondrial molecular clock. It is an area of ongoing research with one study reporting one mutation per 8000 years.

Recent research has shown that mitochondrial DNA haplogroups can influence risk for various diseases and cancers.