sprinting and for quick movements, like in cutting or reining.” While these variations had previ- ously been found in the Thorough- bred, this study took it a step further. “We found the region of the genome very interesting. All the Paints had it. Almost all the Quarter Horses had it. And, within the region were the variants of the gene, which are thought to help the horses be better sprinters. This is the first time we’ve shown that these variants are targets of selective breeding,” Jessica said. “It brings it all back together.”
Bred to Sprint Jessica believes a large portion of
the Paint Horse population carries the sprinting mutation, given the breed’s common roots with the Quarter Horse and decades of selection for muscling that translates into short- but-powerful bursts of speed. “This is a random sample, so it shouldn’t be biased,” she said. “I would doubt that it [sprinting gene] is completely fixed in the Paint Horse breed, but we could speculate that it’s there in high frequency. And we know it’s not in all the Thoroughbreds. Because Thoroughbreds continue to be crossed with Paints, we could predict that some Paint Horses are inheriting the non-speedy gene.” Is genetic testing for this variant in racing-bred Paints the next trend? This might not be necessary. “Based upon our initial survey, I would guess that most of the Paint racehorses are already CC [homo- zygous for the sprinting allele],” she said. “We know that athletes with more
Type 2B muscle fibers are better at quicker, explosive movements. And we know that all Paints and Quarter Horses are not racers, but they were originally bred for sprinting and have been selected to perform quick and powerful movements. That’s why we hypothesize this is found at a high frequency in this random sample that might not all be racehorses.” This discovery is just the tip of the iceberg. Further study is planned.
18 ◆ MARCH 2013 ◆ PAINT HORSE RACING
“We found hundreds of signatures of selection and we are pursuing more now that appear to be important to racing. This gene is probably only one of many that contribute to a horse’s ability to be a good racehorse, either as a sprinter or distance runner,” Jessica said. “This is the first time it has been
shown that these variants were selected for in the Paint and Quarter Horse. And, perhaps more exciting is that this is the first evidence that the variants may cause a change in muscle that we believe makes the horse a bet- ter sprinter.”
Irene Stamatelakys is a special contributor for Paint Horse Racing. To comment on this article, email feedback@apha.com.
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Genome-Wide Analysis Reveals Selection for Important Traits in Domestic Horse Breeds. Published