DNA clue to presidential puzzle
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
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.
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
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
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
Instead, say the researchers, their study makes
Jefferson's claim to be of Welsh extraction much more
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
"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.
It could have been introduced to Europe by the first
modern humans to colonise the continent 40,000 years
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