In their first detailed and comprehensive look at the DNA (search) of chickens, scientists have found that 60 percent of the bird's genes have close cousins in humans. They say such analysis should prove valuable in learning more about the human genome.

But as to the great mystery of why the chicken crossed the road, no answers yet.

"That question is still out there," said Richard K. Wilson (search) of the Washington University School of Medicine in St. Louis.

He's senior author of the chicken DNA analysis, which is presented by an international team of scientists in Thursday's issue of the journal Nature.

The chicken genome — the creature's complete set of DNA — is the first from a bird to be "sequenced," which means scientists identified the 1 billion letters of its DNA code. That job was completed and results made available earlier this year.

Scientists sequence genomes of animals in part because they provide points of comparison for shedding light on the human genome (search). Since the chicken and human genomes have been evolving separately for about 310 million years, it's at a "sweet spot" on the evolutionary tree for such comparisons, Wilson said.

Such analyses can help identify chemical switches that turn genes on and off, for example, he said.

In fact, the new analysis revealed that people have genes related to chicken genes for eggshell proteins, which evidently play a role in bone formation.

Wilson said the chicken genome may also help scientists learn about bird flu, the viral disease found in chickens that might someday set off a deadly worldwide outbreak of human flu. And the genome should also help agricultural scientists track down genes for commercially desirable traits, Jeremy Schmutz and Jane Grimwood of the Stanford Human Genome Center wrote in a Nature commentary.

Wilson and colleagues analyzed the genome of the red jungle fowl, the progenitor of domesticated chickens. Its DNA contains only about one-third as many letters as human DNA does, but roughly the same number of genes, some 20,000 to 23,000.

One surprise was that chickens have more genes related to sensing odors than expected, suggesting a sharper sense of smell than scientists believed, Wilson said. On the other hand, they have fewer genes devoted to sensing tastes than mammals do, especially for bitter sensations, researchers found.

Not surprisingly, chickens were found to lack any version of human genes for milk, saliva and tooth enamel. These genes were, as the scientists put it in a presentation for reporters, as rare as hen's teeth.