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DNA clue to presidential puzzle

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  • Greg Cannon
    http://news.bbc.co.uk/2/hi/science/nature/6332545.stm Tuesday, 6 February 2007, 19:18 GMT DNA clue to presidential puzzle By Paul Rincon Science reporter, BBC
    Message 1 of 1 , Feb 10 8:54 PM
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      http://news.bbc.co.uk/2/hi/science/nature/6332545.stm

      Tuesday, 6 February 2007, 19:18 GMT
      DNA clue to presidential puzzle
      By Paul Rincon
      Science reporter, BBC News

      DNA results from Thomas Jefferson were a mystery
      DNA tests carried out on two British men have shed
      light on a mystery surrounding the ancestry of Thomas
      Jefferson, America's third president.

      In the 1990s, DNA was taken from male relatives of
      Jefferson to see if he fathered a son with one of his
      slaves.

      They found the president had a rare genetic signature
      found mainly in the Middle East and Africa, calling
      into question his claim of Welsh ancestry.

      But this DNA type has now been found in two Britons
      with the Jefferson surname.

      Professor Mark Jobling, from the University of
      Leicester, and colleagues discovered the two British
      Jeffersons possessed the same rare male (or Y)
      chromosome type as the third US president.

      Genetic analysis showed the British men shared a
      common ancestor with Thomas Jefferson about 11
      generations ago. But neither knew of any family links
      to the US.

      The unusual lineage has not been found in white
      Britons before. This discovery scotches any suggestion
      that Jefferson - who was president between 1801 and
      1809 - must have had recent paternal ancestors from
      the Middle East.

      Last month, Professor Jobling's group reported the
      discovery of seven white men from Yorkshire carrying a
      West African Y chromosome.

      Welsh extraction

      The Y chromosome is a package of genetic material
      passed down from father to son, more or less unchanged
      - just like a surname.

      Over many generations, it does accumulate small
      changes in its DNA sequence, allowing relationships
      between different male lineages to be studied.

      Y chromosomes can be classified into broad groups
      (haplogroups) which, to some extent, reflect a
      person's geographical ancestry.

      Certain haplogroups might be common in, for example,
      East Asia but rare in Europe. In Britain, sharing a
      surname raises the likelihood of sharing the same Y
      chromosome type.

      The two men in the latest study had paternal ancestry
      in Yorkshire and the West Midlands respectively.

      Thomas Jefferson's haplogroup - shared with the two
      men from Britain - is known as K2.

      K2 makes up about 7% of the Y chromosome types found
      in Somalia, Oman, Egypt and Iraq. It has now been
      found at low frequencies in France, Spain, Portugal
      and Britain.

      Of the K2s looked at by the study, Jefferson's Y
      chromosome was most similar to that of a man from
      Egypt. But genetic relationships between different K2s
      are poorly understood, and this may have little
      significance.

      Instead, say the researchers, their study makes
      Jefferson's claim to be of Welsh extraction much more
      plausible.

      Common ancestor

      Professor Jobling told BBC News: "Finding that
      Jefferson's Y chromosome was one mutational step away
      from an Egyptian type makes you think 'crikey, could
      he have a relatively recent origin in the Middle
      East?'

      "Our point is that we find, at lower frequencies,
      French, British and Iberian K2s and they are jolly
      diverse. His fits into that picture of a west European
      sub-population of K2."

      The DNA sequences of individual K2s - including those
      from Europe - are quite different from one another.

      This "genetic diversity" has to accumulate over time,
      supporting the idea that Jefferson's haplogroup is not
      a recent introduction into Europe.

      The haplogroup has probably been present for centuries
      in the "indigenous" population of western Europe, says
      Professor Jobling, and is not exclusive to the Middle
      East and Africa.

      Paternity case

      It could have been introduced to Europe by the first
      modern humans to colonise the continent 40,000 years
      ago.

      Another theory concerns the Phoenicians, an ancient
      maritime trading culture that spread out across the
      Mediterranean from their home in what is now Lebanon.
      K2 is relatively common in Lebanon, leading to
      suggestions that European K2s may be descendents of
      these ancient traders.

      In 1998, Jobling and others completed an investigation
      looking at whether Jefferson, main author of the
      Declaration of Independence, fathered a son with Sally
      Hemings, a slave he owned.

      Rumours had long existed that they had one or more
      children. Since Jefferson had no legitimate
      surname-bearing progeny, the team used samples from
      descendents of his paternal uncle.

      They compared these with descendents of Eston Hemings
      Jefferson, Sally's last son. The Y chromosomes
      matched, suggesting Jefferson, or one of his paternal
      relatives, was Eston's father.

      Details appear in the American Journal of Physical
      Anthropology.
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