Reconciling migration models to the Americas with the variation of North American native mitogenomes

In this study we evaluated migration models to the Americas by using
the information contained in native mitochondrial genomes (mitogenomes)
from North America. Molecular and phylogeographic
analyses of B2a mitogenomes, which are absent in Eskimo–Aleut
and northern Na-Dene speakers, revealed that this haplogroup
arose in North America ∼11–13 ka from one of the founder Paleo-
Indian B2 mitogenomes. In contrast, haplogroup A2a,which is typical
of Eskimo–Aleuts and Na-Dene, but also present in the easternmost
Siberian groups, originated only 4–7 ka in Alaska, led to the first Paleo-
Eskimo settlement of northern Canada and Greenland, and contributed
to the formation of the Na-Dene gene pool. However, mitogenomes
also show that Amerindians from northern North America,
without any distinction between Na-Dene and non–Na-Dene, were
heavily affected by an additional and distinctive Beringian genetic
input. In conclusion, most mtDNA variation (along the double-continent)
stems from the first wave from Beringia, which followed the
Pacific coastal route. This was accompanied or followed by a second
inland migratory event, marked by haplogroups X2a and C4c, which
affected all Amerindian groups of Northern North America. Much
later, the ancestral A2a carriers spread from Alaska, undertaking both
a westward migration to Asia and an eastward expansion into the
circumpolar regions of Canada. Thus, the first American founders left
the greatest genetic mark but the original maternal makeup of North
American Natives was subsequently reshaped by additional streams
of gene flow and local population dynamics, making a three-wave
view too simplistic.

http://www.pnas.org/content/110/35/14308.full.pdf+html