Rare White Horse Prancing Around in His Own Special Genes 1 June 2012, by Faye Flam

Rare white horse prancing around in his own special genes 1 June 2012, By Faye Flam

There was no hanky-panky involved when a fairy- around an embryo during development, Galantine- tale white foal was born to two brown Homer said. Such mutations also crop up in mice, Standardbreds at the Four Winds Farm in New pigs, and dogs. Jersey. DNA tests confirm that the snowy foal, born May 6, is a mutant, but that's nothing to be Melanin-producing cells, called melanocytes, form ashamed of. So are most humans, according to a along the proto-spinal cord of an embryo - what's new analysis. called the neural crest, she said. During development, those cells normally receive signals Geneticists and veterinarians say this unusual that prompt them to migrate away and become foal's lack of color comes from a spontaneous or distributed over the embryo. "de novo" mutation - a spelling error in the DNA carried in either the sperm or egg from which he If a mutation interferes with this process, an was conceived. animal can come out white with a smattering of color on the head or along the mane. A few animals "De novo mutations are the fuel of evolutionary with these mutations are also born deaf, Galantino- change," said Joshua Akey, a University of Homer said. That's because some melanin- Washington geneticist. He's been studying de novo producing cells are important for inner-ear mutations in humans, and found hundreds of them. development. Most of these new mutations haven't caused anything as dramatic as this foal's white coat, but There's no indication the white foal is deaf. The Akey says they are probably influencing our mutation he carries is probably located in a gene susceptibility to diseases. called KIT, said Cornell University veterinarian Samantha Brooks. There are 18 known spelling There are no exact numbers for the frequency of errors in this gene that lead to white horses, she white foals, but experts say it's extremely rare to said. Like other horses with KIT mutations, the foal see one crop up spontaneously. Most horses that has some spots of brown along the spine -- the appear white are really pale gray, said Hannah product of cells that were waiting for a signal to Galantino-Homer, a veterinarian and researcher migrate. with the Penn Veterinary School's New Bolton Center. Gray horses tend to fade as they age. Some horses inherit a KIT mutation from a white (That may explain why there are both a pale horse parent, but in this case, the mutation is new and and a white horse ridden by the four horsemen of unique to this horse. the apocalypse - they truly are different colors.) Until now, scientists weren't sure how common White horses can be the product of several such de novo mutations are in our species. In a possible mutations, said Galantino-Homer. Albino study published earlier this month in Science, the horses result from mutations that prevent University of Washington's Akey showed that we production of the compound melanin - a pigment humans are riddled with them. that gives color to skin, hair, and eyes. But such animals usually have pink eyes. This foal's eyes He and his colleagues took DNA from 2,440 are blue. people of both European and African descent and examined just the parts that hold the code for Other mutations that can lead to white animals specific proteins. The result: "We all carry our own prevent pigment-producing cells from migrating personal mutations and an even larger number of

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mutations that are extremely rare," he said.

Some of these may have no biological effects, but he suspects many have a subtle influence on risks for such diseases as Alzheimer's, multiple sclerosis, heart disease, diabetes, cancers, and mental illness.

It's not that we've stopped evolving, Akey said. But the winnowing hand of natural selection has gone easy on our species in recent centuries. Charles Darwin observed that natural selection works because each generation of plants and animals produces many more offspring than can possibly survive. The "struggle for existence," as Darwin described it, leaves just those best equipped to survive and reproduce.

Humans are still subject to evolution, said Akey, but we're experiencing a population explosion. New mutations are appearing much faster than natural selection can filter out the deleterious ones.

If the white foal's mutation is indeed in KIT, then it's dominant, meaning that if he became a sire, it would affect half of his offspring. How far he spreads his new mutation depends on whether his owners think he has a talent for racing. So far, the signs are good, said his owner, Peter Congilose. "He can turn on a dime. He's agile, he's quick.?...?I've never seen a horse that can move like this."

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