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From: Aaron Hill <>
Subject: [yDNAhgI] Scientists Reshape Y Chromosome Haplogroup Tree GainingNew Insights Into Human Ancestry
Date: Tue, 29 Apr 2008 00:46:38 +0000


Scientists
Reshape Y Chromosome Haplogroup Tree Gaining New Insights Into Human
Ancestry
http://www.sciencedaily.com/releases/2008/04/080401184955.htm
ScienceDaily (Apr.
3, 2008) — The Y chromosome retains a remarkable record of human
ancestry, since it is passed directly from father to son. In an
article published in Genome Research scientists have utilized
recently described genetic variations on the part of the Y chromosome
that does not undergo recombination to significantly update and
refine the Y chromosome haplogroup tree.
In 2002, the Y
Chromosome Consortium (YCC) constructed a tree of 153 haplogroups
based upon 243 unique genetic markers. In this report, researchers
led by Dr. Michael Hammer of the University of Arizona recognized the
need to revisit the Y chromosome haplogroup tree and incorporate the
latest data. "The YCC effort in 2002 was a landmark in mapping
the then known 300 or so Y-linked SNPs on a single tree, and getting
the community to use the same nomenclature system," explains
Hammer. "The rate of SNP discovery has continued to increase
over the last several years, as are publications on Y chromosome
origins and affinities. While this new information is useful,
ironically it also brings with it the danger of introducing more
chaos into the field."
Hammer's group
integrated more than 300 new markers into the tree, which allowed the
resolution of many features that were not yet discernable, as well as
the revision of previous arrangements. "The major lineages
within the most common African haplogroup, E, are now all sorted out,
with the topology providing new interpretations on the geographical
origin of ancient sub-clades," describes Hammer. "When one
polymorphism formerly described as unique, but recently shown to have
reversed was replaced by recently reported markers, a sub-haplogroup
of haplogroup O, the most common in China, was considerably
rearranged," explains Fernando Mendez, a co-author of the study.
In addition to
improving the resolution of branches, the latest reconstruction of
the tree allows estimates of time to the most recent common ancestor
of several haplogroups. "The age of [haplogroup] DE is about
65,000 years, just a bit younger than the other major lineage to
leave Africa, which is assumed to be about 70,000 years old,"
says Hammer, describing an example of the fine resolution of age that
is now possible. "Haplogroup E is older than previously
estimated, originating approximately 50,000 years ago."
Furthermore, Hammer
explains that this work has resulted in the addition of two new major
haplogroups, S and T, with novel insights into the ancestry of both.
"Haplogroup T, the clade that Thomas Jefferson's Y chromosome
belongs to, has a Middle Eastern affinity, while haplogroup S is
found in Indonesia and Oceania."
"More SNPs are
being discovered, and we anticipate the rate to increase with the
1000 Genomes Project," says Hammer, referring to the wealth of
human genetic variation data that will soon be available. While this
report represents a significant advance in mapping ancestry by Y
chromosome polymorphisms, it is certain that future discoveries will
necessitate continual revisions to the Y chromosome haplogroup tree,
helping to further elucidate the mystery of our origins.

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