In human genetics, a human mitochondrial DNA haplogroup is a haplogroup
defined by differences in human mitochondrial DNA. Haplogroups are used to
represent the major branch points on the mitochondrial phylogenetic tree.
Understanding the evolutionary path of the female lineage 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.