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Published online: 31
August 2005; | doi:10.1038/news050829-9
Chimpanzee joins the genome club
Genetic sequence could show just how we differ from
other apes.
Michael
Hopkin
Geneticists have finished reading
one of the most important volumes in the library of life: the
DNA of the chimpanzee. Decoding the sequence of our comrade
in apehood may help to answer the age-old question of what makes
us human.
The US-led Chimpanzee Sequencing
and Analysis Consortium, which presents the sequence in this
week's Nature1,
has already begun making such comparisons. By lining the
Pan troglodytes sequence up against the human genome,
it has spotted six areas of our own DNA that have been
rigorously sculpted by natural selection. The areas include
one that contains a gene known to be crucial for that most
human of traits, speech.
"We have targeted regions of genes
that look like they'll be really important for investigating
the differences between chimps and humans," says consortium
member Evan Eichler of the University of Washington School of
Medicine in Seattle.
In the lists
The
chimpanzee joins an extensive roster of species that have been
given the genome-sequencing treatment. The list now numbers in
the hundreds, including a host of bacterial species and
pathogens, the mouse, rice, and family favourites such as the
dog.
 We have targeted regions of genes
that look like they'll be really important for
investigating the differences.  |
Evan
Eichler
University of Washington
School of Medicine,
Seattle | | |
|
| Waiting in the wings are a diverse bunch including
guinea pigs, domestic cats and a motley crew of parasites and
moulds (see 'Decoders target 18 new genomes').
The
chimpanzee consortium assembled its sequence using the now
de rigeur method of whole-genome shotgun sequencing.
This involves cutting up the entire sequence, some 3 billion
letters of code in the chimp's case as in the human genome,
sequencing each section, and reassembling the jigsaw by
computer.
The process has got cheaper and
easier since the human genome was unveiled in 2001, after more
than a decade of struggle costing hundreds of millions of
dollars. The chimp genome cost no more than an estimated US$50
million.
Some 98% of the data came from
blood samples from a single common chimpanzee, called Clint,
who lived at the Yerkes National Primate Research Center in
Atlanta, Georgia. Clint died after a heart failure in January
this year at the tender age of 24; most chimps live into their
50s.
Home truths
So what does Clint's
DNA actually tell us? For a start, humans and chimps are not
quite the close cousins we thought. Crude past comparisons of
our DNA showed that our sequences were between 98.5% and 99%
identical. That is indeed the case when considering
single-letter differences in the DNA code, of which there are
35 million, adding up to about 1.2% of the total
sequence.
But there are other differences,
Eichler says. The two sequences are littered with duplicated
segments that are scattered in different ways in the two
species, he reports in a separate analysis2.
These regions add another 2.7% of difference to the tally. "So
the 1.2% figure is woefully inaccurate," says Eichler.
Much of the difference is seen in genes involved in
the immune system. The contrast suggests that humans and
chimps came up against different diseases during our
evolutionary upbringing, Eichler explains.
The most fertile grounds for
human gene duplications are regions near the ends of chromosomes
called subtelomeres, reports a team led by Barbara Trask of
the Fred Hutchinson Cancer Research Center in Seattle3.
These areas are still poorly understood, she says, and could
tell us more about our own evolution.
But in terms of what
makes us human, the most exciting areas of our genome are six
regions, containing a few hundred genes, that show very little
variation from human to human, but more variation in chimps.
This implies they were important in our evolution. Enticingly,
says Eichler, one of these regions is home to a gene called
FOXP2, which is crucial for producing coherent
speech.
Could this be the thing that really
sets us apart from other apes? Eichler warns against getting
too excited just yet. "I'm a bit pessimistic that this is the
silver bullet," he says. "But it's a part of it."
References
- Chimpanzee Sequencing and Analysis Consortium Nature,
437. 69 - 87 (2005).
- Cheng Z., et al. Nature, 437.
88 - 93 (2005). | Article |
- Linardopoulou E. V., et al. Nature,
437. 94 - 100 (2005). | Article |
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Story from
news@nature.com:
http://news.nature.com//news/2005/050829/050829-9.html | |
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