| By Admin,
on 01-11-2008 09:33
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Researchers
have revealed the complete mitochondrial genome of one of the world's
most celebrated mummies, known as the Tyrolean Iceman or Ötzi. The
sequence represents the oldest complete DNA sequence of modern humans'
mitochondria, according to the report published online on October 30th
in Current Biology, a Cell Press publication. Mitochondria
are subcellular organelles that generate all of the body's energy and
house their own DNA, which is passed down from mother to child each
generation. Mitochondrial DNA thus offers a window into our
evolutionary past. "Through the analysis of a complete
mitochondrial genome in a particularly well-preserved human, we have
obtained evidence of a significant genetic difference between
present-day Europeans and a representative prehistoric human—despite
the fact that the Iceman is not so old—just about 5,000 years," said
Franco Rollo of the University of Camerino in Italy. The
Tyrolean Iceman witnessed the Neolithic-Copper Age transition in
Central Europe more than 5,000 years ago. His mummified corpse was
recovered from an Alpine glacier on the Austro-Italian border in 1991.
In 2000, scientists defrosted the Iceman's body for the first time and
sampled DNA from his intestines. Earlier study of the DNA
showed that he belonged to the lineage, or "subhaplogroup," known as
K1. About 8% of modern Europeans belong to the K haplogroup, meaning
that they share a common ancestor, and that group is divided into two
"subhaplogroups," K1 and K2. The K1 haplogroup, in turn, can be divided
into three clusters. In the new study, the researchers took
advantage of advanced genome-sequencing technologies to shed more light
on the Iceman's genetics. They sequenced his entire mitochondrial
genome and compared that sequence to other published human
mitochondrial DNA sequences to construct his evolutionary (or
phylogenetic) family tree. "The surprise came when we found
that the lineage of the Iceman did not fit any of the three known K1
clusters," Rollo said. His team has informally named the newly
discovered branch on the human family tree "Ötzi's branch." "This
doesn't simply mean that Ötzi had some 'personal' mutations making him
different from the others but that, in the past, there was a group—a
branch of the phylogenetic tree—of men and women sharing the same
mitochondrial DNA," Rollo said. "Apparently, this genetic group is no
longer present. We don't know whether it is extinct or it has become
extremely rare." At least for the moment, he said, that means no one can claim to be "the issue of Ötzi." Human mitochondrial DNA haplogroup
Last update : 01-11-2008 22:58
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