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BBC NEWS
Neanderthal DNA secrets unlocked
By Paul Rincon
Science reporter, BBC News
A genetic breakthrough could help clear up some long-standing
mysteries surrounding our closest evolutionary relatives: the
Neanderthals.
Scientists have reconstructed a chunk of DNA from the genome of a
Neanderthal man who lived 38,000 years ago.
The genetic information they extracted from a thigh bone has allowed
them to identify more than a million building blocks of Neanderthal
DNA so far.
Details of the efforts appear in the journals Nature and Science.
"The sequence data will serve as a DNA time machine," said co-author
Edward Rubin, from the Joint Genome Institute in Walnut Creek,
California, US.
Having a Neanderthal genome will also throw light on our own
evolution
Prof Chris Stringer, Natural History Museum
"[It] will tell us about aspects of Neanderthal biology that we can
never get from their bones and associated artefacts."
Studying the Neanderthal genome will shed light on the genetic
changes
that made our species what it is, after the evolutionary lineages of
Neanderthals and modern humans diverged from one another.
It could also reveal what colour hair, eyes and skin Neanderthals
had,
whether they were capable of modern speech, shed light on aspects of
their brain function and determine whether they contributed to the
modern human gene pool.
'Technical triumph'
Researchers have already sequenced mitochondrial DNA (mtDNA) from 12
Neanderthals. This is DNA from the cell's powerhouses, and which is
passed down from mother to child.
While mtDNA has confirmed that Neanderthals were indeed different
from
us, the information gleaned from it is limited.
THE DNA MOLECULE
The double-stranded DNA molecule is held together by chemical
components called bases
Adenine (A) bonds with thymine (T); cytosine(C) bonds with guanine
(G)
These "letters" form the "code of life"; there are 3.2 billion
base-pairs in the Neanderthal genome
Written in the DNA are genes, which cells use as starting templates
to
make proteins; these sophisticated molecules build and maintain the
body
To answer more detailed questions about our evolutionary cousins,
scientists had to extract DNA that came from the cell's nucleus.
This
nuclear DNA encodes most of an organism's genetic blueprint.
Researchers used cutting-edge DNA sequencing techniques to retrieve
genetic material from the Neanderthal femur found in the Vindija
Cave,
Croatia.
Writing in Nature journal, Professor Svante Paabo and colleagues
describe how they recovered more than one million base-pairs - the
building blocks of DNA - by directly reading the genetic sequence.
In another paper published in Science magazine, Professor Rubin's
team
used a different approach called metagenomics, in which the
fragments
of Neanderthal genetic material were incorporated into bacteria that
were then copied themselves, generating a living "library" of DNA
sequences.
This method resulted in the recovery of 65,250 base-pairs of
Neanderthal DNA.
While direct sequencing allows scientists to recover more genetic
material, it is a random process. The metagenomic approach should
allow scientists to call up specific genetic sequences of interest
from the DNA library in a targeted manner.
Language question
Professor Paabo told BBC science correspondent Pallab Ghosh that he
planned to look at the form of the gene FOXP2 in Neanderthals; this
gene is implicated in the development of language skills and has
undergone evolution in modern humans since our divergence from
chimpanzees.
"We have two little snippets of genes involved in skin and hair
colour, but they don't give any hint of a special variant that would
be of interest," Paabo told BBC News.
The two teams basically agree, within their margins of error, that
the
evolutionary lineages of Neanderthals and modern humans split
somewhere around 500,000 years ago. This fits with previous
estimates
from mtDNA and archaeological data.
Professor Paabo, from the Max Planck Institute for Evolutionary
Anthropology in Leipzig, Germany, and his team also show that
Neanderthals came from a very small ancestral population of about
3,000 individuals.
At their peak, Neanderthals dominated a wide range - stretching from
Britain and Iberia in the west, to Israel in the south and
Uzbekistan
in the east. This stocky, muscular human species was our closest
evolutionary relative.
Modern humans entered Europe about 40,000 years ago; and within
10,000
years, the Neanderthals had largely disappeared from the continent.
By
24,000 years ago, the last survivors had vanished from their refuge
in
the Iberian Peninsula.
Extinct relative
The question of whether modern humans and Neanderthals mated when
they
encountered each other 40,000 years ago is highly controversial.
One US scientist recently suggested modern humans might have
acquired
a variant of the brain gene microcephalin through interbreeding with
Neanderthals.
Edward Rubin's team found no evidence for a Neanderthal contribution
to the modern gene pool, but Professor Paabo's analysis hints at a
possible contribution in the other direction - from modern humans
into
Neanderthals.
The researchers say more extensive sequencing is needed to address
this possibility.
Professor Chris Stringer, from London's Natural History Museum, said
the results "confirm the distinctiveness of the Neanderthals, and
support previous estimates of the divergence time.
"Research will now extend to complete the whole genome of a
Neanderthal and to examine Neanderthal variation through time and
space to compare with ours."
The researchers aim to produce a rough draft of the full Neanderthal
genome sequence over the next two years.
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Story from BBC NEWS:
http://news.bbc.co.uk/go/pr/fr/-/2/hi/science/nature/6146908.stm
Published: 2006/11/15 18:06:08 GMT
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