An international team of researchers has decoded the genome of the domestic horse Equus caballus, revealing a genome structure with remarkable similarities to humans and more than one million genetic differences across a variety of horse breeds. In addition to shedding light on a key part of the mammalian branch of the evolutionary tree, the work also provides a critical starting point for mapping disease genes in horses.
“Horses and humans suffer from similar illnesses, so identifying the genetic culprits in horses promises to deepen our knowledge of disease in both organisms,” said senior author Kerstin Lindblad-Toh, scientific director of vertebrate genome biology at the Broad Institute of MIT and Harvard and a professor of comparative genomics at Uppsala University in Sweden. “The horse genome sequence is a key enabling resource toward this goal.”
In addition to sequencing the genome of a Thoroughbred horse, the researchers also examined DNA from a variety of other horse breeds, including the American quarter horse, Andalusian, Arabian, Belgian draft horse, Hanoverian, Hakkaido, Icelandic horse, Norwegian fjord horse, and Standardbred breeds. The team surveyed the extent of genetic variation both within and across breeds to create a catalog of more than one million single-letter genetic differences (called “single nucleotide polymorphisms” or SNPs).
In a first proof-of-principle of the power of trait mapping in horses, the researchers harnessed the SNP catalog to localize the candidate mutation in the Leopard Complex or “Appaloosa spotting,” in which horses’ coats are mottled with striking patches of white, either with or without colored spots. Horses carrying this trait often suffer from a form of night blindness, a disorder that also afflicts humans. The researchers narrowed the list of genetic suspects in horses to 42 associated SNPs, including two candidate mutations residing near a gene involved in pigmentation.
“This demonstrates the utility of the horse for disease gene mapping,” said Wade. “By making these resources freely available to the scientific community, we hope that many new results will flow from them in the coming years.”