Quarter Horse Genome Sequenced

Quarter Horse Genome Sequenced

Photo: Photos.com

What is a fitting anniversary gift for an international team of geneticists and a Thoroughbred mare called Twilight, who sacrificed a small sample of DNA to have all of her chromosomes sequenced in their entirety five years ago? Why, a second fully sequenced equine genome, of course.

A Texas A&M University research team led by Scott Dindot, PhD, an assistant professor in the Department of Veterinary Pathobiology, recently finished sequencing, or “mapping,” the genome of an 18-year-old Quarter Horse mare called Sugar.

Further, Dindot and colleagues compared Sugar’s genomic map to Twilight’s and found more than 3 million differences, called genetic variants. Many of these differences were present in genes involved in sensory perception, signal transduction (inside and between cells), and immunity.

“We also found that the mare had a different number of copies of some genes relative to Twilight, which has never been reported in horses before,” Dindot relayed. “We recently completed another study looking at these copy number variants (CNVs) to help determine what the differences in copy numbers between different horse breeds mean. For example, CNVs cause many diseases in humans, and we suspect that the same might be true in horses, but more research is needed.”  

In addition, the team reported using updated “second generation” techniques to create the genomic map.

“The technology we used is less expensive than that used for Twilight, and the cost of this technology is decreasing at a remarkable rate; the goal is to be able to sequence a genome for approximately $1,000,” said Dindot. “This is being driven by efforts in human medicine.”

Other than serving as a great conversation starter, what benefit would DNA sequencing bring to the average horse owner?

“Genomic maps will allow us to investigate the genetic basis of disease in horses and to understand the genetic basis of particular traits, such as those distinguishing individual horses and breeds,” explained Dindot. “This technology may also be used to help predict and manage diseases in horses. For example, the (health care) of a horse may be ‘tailored’ depending on its genetic makeup. This is often referred to as ‘personalized medicine.’ ”

According to geneticist Ernie Bailey, PhD, professor of veterinary science at the University of Kentucky's Gluck Equine Research Center, this research is not simply a case of reinventing the wheel.

“Having a map of more than one horse’s genome is important," he said. "It is the equivalent of having the engineering specifications for a car. Does it matter which car the specifications are for? After all, all cars have wheels, engines, doors, etc., but each model of car is unique

“The horse’s genome sequence is the same (idea)," he continued. "In general all horses share DNA sequence and organization but there can be major rearrangements in the genes from horse to horse.”

An excellent example of major rearrangements of DNA in horses is the tobiano spotting pattern caused by a large section of DNA (3 million base pairs) on equine chromosome 3 that runs in the opposite direction on Sugar’s DNA when compared to Twilight's.

“Scott’s publication is another landmark for horse research and heralds a new approach to discovery," Bailey added. "At the recent horse genome workshop meeting in January 2012, scientists from laboratories around the world reported that whole genome sequencing of seven more horses was either completed or underway. As we learn more about these and other horse genomes, we will be able to discover what makes a successful performance horse. Returning to the car analogy, we will be able to ‘look under the hood.’ ”

“In collaboration with other groups, we will continue to sequence more horse genomes to catalog most of the genetic variation in horses. We will also continue to investigate CNVs to understand their role in disease and traits in horses,” Dindot added.

The full length study describing Dindot et al.’s work is scheduled to be published in the journal BMC Genomics, and additional information on the Horse Genome Project is available online.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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