| dc.description.abstract | The recent availability of large-scale sequence
data for the human Y chromosome has revolutionized analyses
of and insights gained from this non-recombining,
paternally inherited chromosome. However, the studies to
date focus on Eurasian variation, and hence the diversity
of early-diverging branches found in Africa has not been
adequately documented. Here, we analyze over 900 kb
of Y chromosome sequence obtained from 547 individuals
from southern African Khoisan- and Bantu-speaking
populations, identifying 232 new sequences from basal
haplogroups A and B. We identify new clades in the phylogeny,
an older age for the root, and substantially older
ages for some individual haplogroups. Furthermore, while haplogroup B2a is traditionally associated with the spread
of Bantu speakers, we find that it probably also existed
in Khoisan groups before the arrival of Bantu speakers.
Finally, there is pronounced variation in branch length
between major haplogroups; in particular, haplogroups
associated with Bantu speakers have significantly longer
branches. Technical artifacts cannot explain this branch
length variation, which instead likely reflects aspects of the
demographic history of Bantu speakers, such as recent population
expansion and an older average paternal age. The
influence of demographic factors on branch length variation
has broader implications both for the human Y phylogeny
and for similar analyses of other species. | en_US |
