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Last Updated: Thursday, 9 December 2004, 00:15 GMT
Chicken gives up genetic secrets
Magazine cover (Nature)
The product of scientists working in 49 countries
Scientists have published a detailed analysis of the chicken genome, the biochemical "code" in the bird's cells that makes the animal what it is.

The data should help us understand better our own biology and may give us fresh insight on avian-borne diseases such as salmonella and bird flu.

It could also lead to a step-change in the food industry with the development of more productive and healthier birds.

The International Chicken Sequencing Consortium reports its work in Nature.

"The chicken is the first bird as well as the first agricultural animal to have its genome sequenced and analysed," said Richard Wilson, of the Washington University School of Medicine in St Louis, US, and a lead researcher on the project.

Sharp focus

The primary subject for the study was the red jungle fowl (Gallus gallus), the wild species from which domestic poultry was bred several thousand years ago.

CHICKEN DNA
Graphic, BBC
The double-stranded DNA molecule is held together by four chemical components, or bases
Adenine (A) bonds with thymine (T); cytosine(C) bonds with guanine (G)
Groupings of these "letters" form the "code of life". There are about 1.1 billion base-pairs in the chicken genome wound into 40 distinct bundles, or chromosomes
Written in the DNA are roughly 20-23,000 genes, which chicken cells use as starting templates to make proteins. These sophisticated molecules build and maintain the animal's body
In the human genome, there are 3 billion base-pairs and 20-25,000 genes
For their research samples, scientists used one particular hen, now more than seven years old and living out its days on a Michigan research facility utterly unaware of its place in history.

The consortium's investigation shows the chicken to have approximately one billion base-pairs, or bonded "letters", of DNA. This compares with roughly three billion found in mammals, such as the human.

The analysis reveals that just 2.5% of the human code can be matched to chicken DNA.

It is an important finding. This small portion contains genes that have been largely preserved over the 310 million years since humans and birds shared a common ancestor.

"We believe that the bits of the genome that are most resilient to change are those that have been most crucial to our survival throughout evolutionary history," said Chris Ponting, from Oxford University, UK, who has been comparing the chicken and human data.

"This 2.5% corresponds to 70 million letters of DNA and among these is where we can look first for mutations linked to human disease. In effect, the chicken genome has helped us condense the human genome to something more manageable."

Future tools

The chicken has long had important roles in science. Developmental biologists have used it to study embryonic growth.

Biomedical researchers have also made important advances in immunology and cancer research by studying chickens. The first tumour virus and cancer gene were identified in chicken research.

All of these areas will be advanced by knowledge of the bird's genome.

Chicken, AP
It should be a big help to the poultry industry
Of particular interest currently is the threat posed to human health by illnesses that can afflict both chickens and humans, such as bird flu.

The new data may give science an insight into the genetics of resistance, something that would perhaps help researchers develop better vaccines or identify the poultry strains least likely to be susceptible to pathogens.

"What this research does give us is an incredible set of tools to study the genetic variation of these birds," said Ewan Birney, from the European Bioinformatics Institute in Cambridge, UK.

"We know there's a lot of difference between different strains of chicken and different types of birds in the way they transmit these diseases, but we don't know which genes are really involved in helping prevent transmission of, say, the flu virus," he told BBC News.

"With the genome and the genetic tools that that gives us, we'll have a much better platform to do this sort of research in the future."

Other researchers expect there to be big pay-offs for agriculture, too, with the possibility of identifying the underlying biochemical drivers of traits such as bigger eggs and tastier, leaner meat.

On a pure research level, though, there are some real gems in the chicken genome.

These include the realisation that the birds have a keen sense of smell. Scientists can also see genes related specifically to feathers, claws and scales - code sequences that are absent in humans.




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