Scientists map horse's DNA

February 09, 2007|By Bryn Nelson | Bryn Nelson,Newsday

Scientists have assembled the genetic blueprint of a thoroughbred mare, a rough draft of its entire DNA sequence that may point the way toward a better understanding of equine evolution, physiology and the dozens of diseases found in both horses and humans.

Claire Wade, a lead member of the sequencing team and a senior research scientist at the Broad Institute in Cambridge, Mass., said the assembled genome still contains sizable gaps and has not been thoroughly analyzed. Nevertheless, she and other researchers said its estimated 2.7 billion units, or letters, of DNA should provide a wealth of new information.

"It takes us from the relative dark ages of genetics to the relative forefront," said Dr. Doug Antczak, a professor of equine medicine at Cornell University in Ithaca, N.Y.

Scientists isolated the DNA from Twilight, a mare housed at Cornell and bred to help Antczak understand how horse fetuses and placentas can successfully evade or defend against the mother's immune system. Far beyond his own studies, however, Antczak said Twilight's DNA may lay the foundation for research efforts around the world.

Like humans, for example, horses are susceptible to the West Nile virus and must contend with allergies and arthritis. Some suffer from neurological or muscular disorders. And Arabian horses can inherit a form of severe combined immunodeficiency, more commonly called "bubble boy" disease.

So far, researchers have found more than 80 genetically linked diseases common to horses and humans.

Wade said racing horses may grant a better understanding of physiology, perhaps enabling veterinarians to help them and other breeds more easily recover from injuries. And since, like us, horses have been preyed upon by bears, wolves and predatory cats, they may teach us a thing or two about the biological basis of caution. "Horses do get anxious," she said. "Because they're prey animals, they do have to be very aware."

The $15 million sequencing effort, funded by the National Human Genome Research Institute, suggests we share about 85 percent of our genetic information with horses. Like us, they are thought to possess fewer than 20,000 genes, though their 64 chromosomes - half inherited from each parent - easily bests our 46.

The new genome may also enable researchers to peer into the evolutionary past of a mammalian group that includes everything from tapirs and rhinoceroses to horses and zebras.

A related effort has used the DNA of seven distinct breeds, from Arabians and Akel Tekes to Icelandic and quarter horses, to compare their genetic differences. A resulting map pinpoints the locations of 1 million variable spots, known as single nucleotide polymorphisms, which should provide a better view of equine diversity.

Bryn Nelson writes for Newsday.

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