Family Tree DNA's haplogroup description of U2:
The mitochondrial super-haplogroup U encompasses haplogroups U1-U7 and haplogroup K. Haplogroup U2 is found distributed in the Near East and Europe, though it is maintained a rather low frequency throughout. This sparse, yet widespread, dissemination, when combined with the presence of an allied haplogroup found in India, suggests that haplogroup U2 is very old, and was likely an early lineage of the super-haplogroup U, which arose greater than 50,000 years ago.
Excerpts from Dr. Spencer Wells' latest book "Deep Ancestry":
Ancestral line "Eve" -> L1/L0 -> L2 -> L3 -> N -> R -> U
Because of the great genetic diversity found in haplogroup U, it is likely that it developed around 50,000 years ago. Today, haplogroup U members are found in Europe and the eastern Mediterranean at frequencies of almost 7 percent of the population.
DNA analysed from early European
BBC News - 1 Jan 2010
Characterization of human control region sequences for Spanish individuals in a forensic mtDNA data set
J. Alvarez, et al.
Abstract only available at link, e-mail administrator for full-text article. U2 haplogroup excerpt: "U is the second most common haplogroup in the study (n = 51, 16%). Helgason, et al.  defined a subgroup, U2, based on the presence of 16051G and 16129C and there were four (1.3%) individuals with those characters in the Spanish data set."
mtDNA polymorphisms in five French groups: importance of regional sampling
by V. Dubut, et al. Contains sampling data on U2 found in the regions of Caux, Bray, and Pe´rigord-Limousin.[pg 4]
A database of mitochondrial DNA hypervariable regions I and II
sequences of individuals from Slovakia by I. Lehocky, et al. Pg 4 
U2e 051-092-129GC-319-362-391 73-152-199-217-263-309.1C-309.2C-315.1C
U2e 051-093-129GC-189-362 73-152-217-263-309.1C-315.1C
U2e 051-129GC-189-256-311 73-152-217-263-315.1C-340
Haplogroup U2 Volunteer DNA Project Administrators
The U2 Haplogroup mtDNA Project is an independent genealogical research study and receives no grant underwriting. Participants are responsible for the costs of their own tests.
The project was organized as a cooperative effort among those who wish to explore genetic testing to advance their knowledge of deep and recent family backgrounds.
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