Haplogroup A (Y-DNA)

Haplogroup A is a human Y-chromosome DNA haplogroup, which includes all living human Y chromosomes. Bearers of extant sub-clades of haplogroup A are almost exclusively found in Africa (or among the African diaspora), in contrast with haplogroup BT, bearers of which participated in the Out of Africa migration of early modern humans. The known branches of haplogroup A are A00, A0, A1a, and A1b1; these branches are only very distantly related, and are not more closely related to each other than they are to haplogroup BT.

Origin

Though there are terminological challenges to define it as a haplogroup, haplogroup A has come to mean "the foundational haplogroup" (viz. of contemporary human populations); it is not defined by any mutation, but refers to any haplogroup which is not descended from the haplogroup BT; in other words, it is defined by the absence of the defining mutation of that group (M91). By this definition, haplogroup A includes all mutations that took place between the Y-chromosomal most recent common ancestor (estimated at some 270 kya) and the mutation defining haplogroup BT (estimated at some 140–150 kya), including any extant subclades that may yet to be discovered.

Bearers of haplogroup A (i.e. absence of the defining mutation of haplogroup BT) have been found in Southern Africa's hunter-gatherer inhabited areas, especially among the San people. In addition, the most basal mitochondrial DNA L0 lineages are also largely restricted to the San. However, the A lineages of Southern Africa are sub-clades of A lineages found in other parts of Africa, suggesting that A sub-haplogroups arrived in Southern Africa from elsewhere.

The two most basal lineages of haplogroup A, A0 and A1 (prior to the announcement of the discovery of haplogroup A00 in 2013), have been detected in West Africa, Northwest Africa and Central Africa.