DNA code reveals chicken odyssey
Scientists say they have unravelled the genetic code of the chicken, an evolutionary trek that began before the age of the dinosaurs and led to the emergence of the world's most important bird today.
The secrets of the chicken genome could lead to super-hens - new breeds which will lay more eggs, have more meat and be more resistant to disease than any poultry that has walked the earth.
There could be health benefits too, by helping the fight against bird flu, a disease that could threaten millions of people.
An international consortium took a DNA sample from the red jungle fowl (Latin name Gallus gallus), which is believed to be the wild ancestor of domestic chickens, and decrypted its code.
The draft, which appears in this week's issue of the British journal Nature, comprises about a billion base pairs, the "rungs" which make the ladder in the double helix of DNA.
Gallus gallus - the first bird to have its DNA code sequenced - has an estimated 20,000-23,000 genes, which puts the total in the same ballpark as that for Man, the authors say.
"About 60 per cent of the chicken protein-coding genes have human equivalents," says one of the researchers, Peer Bork of Germany.
Indeed, a closer scrutiny shows that humans and chickens - indeed, all vertebrates - shared a common ancestor around 310 million years ago, even before the dinosaurs emerged, they say.
Archaeopteryx, considered to be the first bird, popped up some 150 million years later.
Today, humans and chickens still share some sequences of DNA but the rest of our respective codes is different.
They have been sculpted by evolutionary pressures that ruthlessly weed out genes which hamper survival of the species.
In a parallel study, also published in Nature, gene sleuths compared the genome of Gallus gallus with three standard breeds of domestic chicken - a broiler, a layer and a Chinese silkie.
The scrawny, feisty Gallus and the chubby, passive broiler are so different that they might seem a species apart.
But genetically, they are astonishingly similar.
Variations in tiny stretches of code can make vast differences.
For example, a variation in just a single gene, GGA1, accounts for nearly a third of the difference in adult body weight between Gallus and the white leghorn breed, the study says.
Intensive poultry farming began about half a century ago, leading to the creation of highly specialised breeds, which - in sometimes controversial conditions - deliver more meat and eggs than any chickens in history.
Today, billions of chickens are raised and slaughtered each year.
Pinpointing useful genes and incorporating them safely into existing chicken breeds opens up exciting possibilities for feeding the world's fast-growing population.
Chicken breeding "represents one of the most remarkable examples of directed evolution," the main study, carried out by the International Chicken Genome Sequencing Consortium, says.
"Even after 50 years of intensive selection, annual genetic progress in production traits remains undiminished."
The chicken genome could also help the battle against avian influenza, the source of a health scare in South-East Asia.
The World Health Organisation (WHO) fears that if bird flu spreads among humans, it could mutate into a dangerous agent that could kill millions of people.
"We really sequenced the chicken to understand our own human genome, that was the big motivation," study co-author Ewan Birney of the European Bioinformatics Institute, Cambridge, told AFP.
"But it also gives us great tools to understand variations among chickens. We should be able to see which strains of chickens are transmitting more of the flu and are more susceptible to it, and precisely which part of that genome is perhaps responsible for that.
"If we found strains that are more at risk, we could advise people against raising them."
