Genetic Mutation Behind Albino Donkeys Pinpointed

Genetic Mutation Behind Albino Donkeys Pinpointed

The albino donkeys protect themselves from the sun in prison buildings that date from the early 1900s, when the island was isolated as a detention center for war prisoners, mafia leaders, and terrorists before closing in 1997.

Photo: Courtesy Valerio Joe Utzeri

Imagine a vast herd of white donkeys, grazing against a spectacular Mediterranean backdrop on an island off the coast of Italy.

No need to imagine. This scene exists. And while it evokes remarkable beauty “where nature and history merge in a fascinating landscape,” said one scientist, it also prods the curiosity of local biologists. How is it that these fair-colored animals have evolved and now thrive in a sun-scorching world that, theoretically, could have eradicated them centuries ago?

An albinism mutation—creating the pigmentless “albino” effect—probably occurred in a donkey on the island of Asinara, Italy, several centuries ago, said Luca Fontanesi, PhD, of the University of Bologna Department of Agricultural and Food Sciences, in Italy. And inbreeding due to the herd’s isolation likely allowed the albinism to continue in later generations.

Today, just over 100 white donkeys live along with colored donkeys on the uninhabited island of Asinara, which literally means “donkey-inhabited” in Italian. They’ve had no human intervention for more than 100 years.

Fontanesi and his fellow researcher, Valerio Joe Utzeri, PhD candidate at the University of Bologna, who originally hails from Sardinia (another Italian island in the Mediterranean), sequenced a specific gene—the TYR gene, which they assumed was related to albinism based on prior research—in 13 of these donkeys. Seven of them were white Asinara albino donkeys and the other six were colored.

In the white donkeys, the researchers found a missense mutation (a change in one amino acid in a protein in a single nucleotide). The donkeys' mutation results in a particular protein not bonding to copper atoms as it normally would, Fontanesi said. As a result, the animals do not develop pigmentation; instead, they have white skin and hair, white eyelashes, and blue eyes (an absence of color in eyes gives them a bluish hue). The white animals had two copies of the allele (gene variant), meaning they had received one from each parent and that the genetic code is recessive.

The researchers genotyped another 82 donkeys and confirmed their findings: All white donkeys had double copies of the mutated allele, whereas colored donkeys had one or no copy.

“It’s important to know the exact mutation of an unusual characteristic—in this case, albinism—as it allows us to manage the white population and also estimate the actual frequency of the mutated allele in donkeys that might be carriers of that allele,” Fontanesi said. From a biological point of view, finding a mutation in a protein also helps scientists better understand that protein’s purpose. In this case, for example, the researchers now know that the protein affected by the mutation is one that’s involved in pigmentation.

“It’s also fascinating to simply research something so curious, this strange situation that’s not common in feral or wild populations,” he added. “It’s quite puzzling to have an albino feral population in a Mediterranean island where sun radiation might be very high; it could be deleterious in such environment.”

Fontanesi said the albino donkeys protect themselves from the sun in prison buildings that date from the early 1900s, when the island was isolated as a detention center for war prisoners, mafia leaders, and terrorists before closing in 1997. The island became a national park in 1999, where visitors can see the donkeys in their “incredible environment,” he said.

The study, “The albinism of the feral Asinara white donkeys (Equus asinus) is determined by a missense mutation in a highly conserved position of the tyrosinase (TYR) gene deduced protein,” was published in Animal Genetics

About the Author

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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