These groups are called haplogroups.

Over the course of human prehistory, as populations expanded across the globe, different haplogroups accumulated in different geographic regions.

The founding populations of different continents carried different haplogroups, and the specific haplogroups present in a population reflect the ancestral history of that population’s maternal lineage.

In Native American populations, genetic research has identified five major mitochondrial haplogroups that are found across the hemisphere — designated A, B, C, D, and X.

These five haplogroups account for the vast majority of the maternal-line genetic diversity present in Indigenous American populations, and they all reflect an ultimate ancestry from the population that crossed into the Americas from northeastern Asia during the late Pleistocene.