@@ Scientists hail 'historic' mapping of chimp's genome @@
- From: "Arash" <A7000@xxxxxxxxxxx>
- Date: Wed, 31 Aug 2005 14:27:13 -0400
National Human Genome Research Institute (NHGRI)
August 31, 2005
New Genome Comparison Finds Chimps, Humans Very Similar at the DNA Level
The first comprehensive comparison of the genetic blueprints of humans and
chimpanzees shows our closest living relatives share perfect identity with 96 percent
of our DNA sequence, an international research consortium reported today.
In a paper published in the September 1st issue of the journal Nature, the Chimpanzee
Sequencing and Analysis Consortium, which is supported in part by the National Human
Genome Research Institute (NHGRI), one of the National Institutes of Health (NIH),
describes its landmark analysis comparing the genome of the chimp (Pan troglodytes)
with that of human (Homo sapiens).
"The sequencing of the chimp genome is a historic achievement that is destined to
lead to many more exciting discoveries with implications for human health", said
NHGRI director Francis Collins. "As we build upon the foundation laid by the Human
Genome Project, it?s become clear that comparing the human genome with the genomes of
other organisms is an enormously powerful tool for understanding our own biology".
The chimp sequence draft represents the first non-human primate genome and the fourth
mammalian genome described in a major scientific publication. A draft of the human
genome sequence was published in February 2001, a draft of the mouse genome sequence
was published in December 2002 and a draft of the rat sequence was published in March
2004. The essentially complete human sequence was published in October 2004.
"As our closest living evolutionary relatives, chimpanzees are especially suited to
teach us about ourselves," said the study?s senior author, Robert Waterston, chair of
the Department of Genome Sciences of the University of Washington School of Medicine
in Seattle. "We still do not have in our hands the answer to a most fundamental
question: What makes us human? But this genomic comparison dramatically narrows the
search for the key biological differences between the species".
The 67 researchers who took part in the Chimp Sequencing and Analysis Consortium
share authorship of the Nature paper. Most of the work of sequencing and assembling
the chimp genome was done at the Broad Institute of the Massachusetts Institute of
Technology and Harvard University, Cambridge, Mass., and the Washington University
School of Medicine in Saint Louis.
The DNA used to sequence the chimp genome came from the blood of a male chimpanzee
named Clint at theYerkes National Primate Research Center in Atlanta. Clint died last
year from heart failure at the relatively young age of 24, but two cell lines from
the primate have been preserved at the Coriell Institute for Medical Research in
Camden, New Jersey
The consortium found that the chimp and human genomes are very similar and encode
very similar proteins. The DNA sequence that can be directly compared between the two
genomes is almost 99% identical. When DNA insertions and deletions are taken into
account, humans and chimps still share 96% of their sequence. At the protein level,
29% of genes code for the same amino sequences in chimps and humans. In fact, the
typical human protein has accumulated just one unique change since chimps and humans
diverged from a common ancestor about 6 million years ago.
To put this into perspective, the number of genetic differences between humans and
chimps is approximately 60 times less than that seen between human and mouse and
about 10 times less than between the mouse and rat. On the other hand, the number of
genetic differences between a human and a chimp is about 10 times more than between
any two humans.
The researchers discovered that a few classes of genes are changing unusually quickly
in both humans and chimpanzees compared with other mammals. These classes include
genes involved in perception of sound, transmission of nerve signals, production of
sperm and cellular transport of electrically charged molecules called ions.
Researchers suspect the rapid evolution of these genes may have contributed to the
special characteristics of primates, but further studies are needed to explore the
possibilities.
The genomic analyses also showed that humans and chimps appear to have accumulated
more potentially deleterious mutations in their genomes over the course of evolution
than have mice, rats and other rodents. While such mutations can cause diseases that
may erode a species? overall fitness, they may have also made primates more adaptable
to rapid environmental changes and enabled them to achieve unique evolutionary
adaptations, researchers said.
Despite the many similarities found between human and chimp genomes, the researchers
emphasized that important differences exist between the two species.
About 35 million DNA base pairs differ between the shared portions of the two
genomes, each of which, like most mammalian genomes, contains about 3 billion base
pairs.
In addition, there are another 5 million sites that differ because of an insertion or
deletion in one of the lineages, along with a much smaller number of chromosomal
rearrangements. Most of these differences lie in what is believed to be DNA of little
or no function. However, as many as 3 million of the differences may lie in crucial
protein-coding genes or other functional areas of the genome.
"As the sequences of other mammals and primates emerge in the next couple of years,
we will be able to determine what DNA sequence changes are specific to the human
lineage. The genetic changes that distinguish humans from chimps will likely be a
very small fraction of this set", said the study?s lead author, Tarjei S. Mikkelsen
of the Broad Institute of MIT and Harvard. Among the genetic changes that researchers
will be looking for are those that may be related to the human-specific features of
walking upright on two feet, a greatly enlarged brain and complex language skills.
Although the statistical signals are relatively weak, a few classes of genes appear
to be evolving more rapidly in humans than in chimps. The single strongest outlier
involves genes that code for transcription factors, which are molecules that regulate
the activity of other genes and that play key roles in embryonic development.
A small number of other genes have undergone even more dramatic changes. More than 50
genes present in the human genome are missing or partially deleted from the chimp
genome. The corresponding number of gene deletions in the human genome is not yet
precisely known. For genes with known functions, potential implications of these
changes can already be discerned.
For example, the researchers found that three key genes involved in inflammation
appear to be deleted in the chimp genome, possibly explaining some of the known
differences between chimps and humans in respect to immune and inflammatory response.
On the other hand, humans appear to have lost the function of the caspase-12 gene,
which produces an enzyme that may help protect other animals against Alzheimer?s
disease.
"This represents just the tip of the iceberg when it comes to exploring the genomic
roots of our biological differences," said one of the study?s co-authors LaDeana W.
Hillier of the Genome Sequencing Center at Washington University School of Medicine.
"As more is learned about other functional elements of the genome, we anticipate that
other important differences outside of the protein-coding genes will emerge."
Armed with the chimp sequence, researchers also scanned the entire human genome for
deviations from normal mutation patterns. Such deviations may reveal regions of
"selective sweeps," which occur when a mutation arises in a population and is so
advantageous that it spreads throughout the population within a few hundred
generations and eventually becomes "normal."
The researchers found six regions in the human genome that have strong signatures of
selective sweeps over the past 250,000 years. One region contains more than 50 genes,
while another contains no known genes and lies in an area that scientists refer to as
a "gene desert." Intriguingly, this gene desert may contain elements regulating the
expression of a nearby protocadherin gene, which has been implicated in patterning of
the nervous system. A seventh region with moderately strong signals contains the
FOXP2 and CFTR genes. FOXP2 has been implicated in the acquisition of speech in
humans. CFTR, which codes for a protein involved in ion transport and, if mutated,
can cause the fatal disease cystic fibrosis, is thought to be the target of positive
selection in European populations.
The chimp and human genome sequences, along with those of a wide range of other
organisms such as mouse, honey bee, roundworm and yeast, can be accessed through the
following public genome browsers: (http://www.ncbi.nih.gov/Genbank) at NIH's National
Center for Biotechnology Information (NCBI); the UCSC Genome Browser
(http://www.genome.ucsc.edu) at the University of California at Santa Cruz; the
Ensembl Genome Browser (http://www.ensembl.org) at the Wellcome Trust Sanger
Institute and the EMBL-European Bioinformatics Institute; the DNA Data Bank of Japan
(http://www.ddbj.nig.ac.jp); and EMBL-Bank (http://www.ebi.ac.uk/embl/index.html) at
the European Molecular Biology Laboratory's Nucleotide Sequence Database.
A high resolution version of the image displayed on this page is available at:
http://www.genome.gov/10005141
Comparative Genomics
http://www.genome.gov/11509542
Nature
September 1, 2005
Initial sequence of the chimpanzee genome and comparison with the human genome
http://www.genome.gov/Pages/Research/DIR/Chimp_Analysis.pdf (1MB)
NHGRI is one of 27 institutes and centers at the NIH, an agency of the Department of
Health and Human Services. The NHGRI Division of Extramural Research supports grants
for research and for training and career development at sites nationwide. Additional
information about NHGRI can be found at its Web site http://www.genome.gov
http://www.genome.gov/15515096
.
- Prev by Date: 16 photographs by al-Farrob - updating weekly now
- Next by Date: Iraq shiite stampede
- Previous by thread: 16 photographs by al-Farrob - updating weekly now
- Next by thread: Iraq shiite stampede
- Index(es):
Relevant Pages
|
