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### For release after 1 p.m. ET, April 14, 2003

### Comparative Genomics

Sequencing the genomes of the human, the mouse and a wide variety of
other organisms -- from yeast to chimpanzees -- is driving the
development of an exciting new field of biological research called
comparative genomics.

By comparing the finished reference sequence of the human genome with
genomes of other organisms, researchers can identify regions of
similarity and difference. This information can help scientists better
understand the structure and function of human genes and thereby develop
new strategies to combat human disease. Comparative genomics also
provides a powerful tool for studying evolutionary changes among
organisms, helping to identify genes that are conserved among species,
as well as genes that give each organism its unique characteristics.

Using computer-based analysis to zero in on the genomic features that
have been preserved in multiple organisms over millions of years,
researchers will be able to pinpoint the signals that control gene
function, which in turn should translate into innovative approaches for
treating human disease and improving human health. In addition, the
evolutionary perspective may prove extremely helpful in understanding
disease susceptibility. For example, chimpanzees do not suffer from some
of the diseases that strike humans, such as malaria and AIDS, even
though chimps' DNA sequence is 98.8 percent identical to ours. A
comparison of the sequence of genes involved in disease susceptibility
may reveal the reasons for this species barrier, thereby suggesting new
pathways for prevention of human disease.

In addition to its implications for human health and well-being,
comparative genomics may benefit the animal world as well. As sequencing
technology grows easier and less expensive, it will likely find wide
applications in zoology, agriculture and biotechnology as a tool to
tease apart the often-subtle differences among animal species. Such
efforts might also possibly lead to the rearrangement of our
understanding of some branches on the evolutionary tree, as well as
point to new strategies for conserving rare and endangered species.

Although living creatures look and behave in many different ways, all of
their genomes consist of DNA, the chemical chain that makes up the genes
that code for thousands of different kinds of proteins. Precisely which
protein is produced by a given gene is determined by the sequence in
which four chemical building blocks -- adenine (A), thymine (T),
cytosine (C) and guanine (G) -- are laid out along DNA\'s double-helix
structure.

In order for researchers to use an organism\'s genome most efficiently
in comparative studies, data about its DNA must be in large, contiguous
segments, anchored to chromosomes and, ideally, fully sequenced.
Furthermore, the data needs to be organized to allow easy access for
researchers using sophisticated computer software to conduct high-speed
analyses.

The successful sequencing of the human genome and the recent draft
assemblies of the mouse and rat genomes have demonstrated that
large-scale sequencing projects can generate high-quality data at a
reasonable cost. As a result, the interest in sequencing the genomes of
many other organisms has risen dramatically.

In addition to the human *(Homo sapiens)* and mouse *(Mus musculus)*,
organisms whose genomes have been sequenced include: rat *(Rattus
norvegicus)*; two fruit flies *(Drosophila melanogaster* and *D.
pseudoobscura)*; two roundworms *(Caenorhabditis elegans* and *C.
briggsae)*; yeast *(Saccharomyces cerevisiae)* and several other fungi;
a malaria-carrying mosquito *(Anopheles gambiae)* along with a
malaria-causing parasite *(Plasmodium falciparum)*; two sea squirts
*(Ciona savignyi* and *C. intestinalis)*; a long list of microbes; and a
couple of plants, including mustard weed *(Arabidopsis thaliana)* and
rice *(Oryza sativa)*. Sequencing work is well underway on the honeybee
*(Apis mellifera)*, and is just getting started or expected to begin
soon on the chimpanzee *(Pan troglodytes)*, the cow *(Bos taurus),* the
dog *(Canis familiaris)* and the chicken *(Gallus gallus).*

The fledgling field of comparative genomics has already yielded dramatic
results. For example, a March 2000 study comparing the fruit fly genome
with the human genome discovered that about 60 percent of genes are
conserved between fly and human. Or, to put it simply, the two organisms
appear to share a core set of genes. Researchers have found that
two-thirds of human genes known to be involved in cancer have
counterparts in the fruit fly. Even more surprisingly, when scientists
inserted a human gene associated with early-onset Parkinson\'s disease
into fruit flies, they displayed symptoms similar to those seen in
humans with the disorder, raising the possibility the tiny insects could
serve as a new model for testing therapies aimed at Parkinson\'s.

NHGRI created a priority-setting process in 2001 to make rational
decisions about the many requests being brought forward by various
communities of scientists, each championing the animals used in its own
research. The priority-setting process, which does not result in new
grants for sequencing the organisms, is based on the medical,
agricultural and biological opportunities expected to be created by
sequencing a given organism. For more information on the status of model
organisms in the priority-setting process, go to NHGRI's Web site at:
[www.genome.gov/10002154](http://www.genome.gov/10002154).

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