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The Horse, of Course: Horse Genome Mapped
By Nancy Touchette

When Bhanu P. Chowdhary watches the Triple Crown races this spring, he’ll be thinking about more than thoroughbreds, jockeys, and mint juleps. He’ll be thinking about genomes.


Chowdhary, a horse researcher at Texas A&M University in College Station, leads an international collaboration to map and eventually sequence the horse genome. The group has just published a new gene map of the horse and compared it the human genome, revealing genetic similarities that could benefit researchers studying both species.

“The whole purpose is to develop a roadmap for studying the horse, so we can develop associations between genes and what we see in disease,” says Chowdhary. “But before we can identify mutations that cause disease, we need to know their location.”

The group’s primary interest in mapping the horse is to understand the genes that contribute to genetic disorders, reproduction, disease resistance, and equine health in general. As a bonus, horse enthusiasts may be interested in the genes that control other traits, such as coat color and size.

Studying the horse genome may also help researchers better understand human disease. Humans are more similar to the horse than to the laboratory mouse, and approximately 80 known conditions are similar between horse and humans, such as arthritis.

For example, people with Down syndrome have an extra copy of chromosome 21, a condition called trisomy 21. This chromosome corresponds to chromosome 26 in horses, and like humans, some horses are born with an extra chromosome 26 (trisomy 26).

The horse genome has 32 pairs of chromosomes and contains about the same amount of DNA as the human genome (three billion base pairs). The horse genome appears to include vast regions of DNA that do not code for genes, as does the human genome.

One of the most interesting horse chromosomes is 22. It is nearly identical to human chromosome 20 and part of mouse chromosome 2. These three regions not only share most of the same genes, but the genes also appear in the same order among all three species.

The X chromosome is also almost identical in terms of the order of genes between horses and human. Horse chromosome 11 matches human 17.

Despite the interest in picking a Triple Crown winner, Chowdhary doubts that the horse genome will be very useful for that purpose.

“Races are not won by a single gene,” Chowdhary says. “Athleticism in humans, as well as in horses, is determined by many genes interacting with each other and their environment. You can’t pinpoint a certain gene and say, ‘This horse will be a winner.’”

Even if genomics could be used to predict racing success, Chowdhary adds, it would have undesirable consequences. “If we were able to pick genes to predict winners, the racing industry would collapse.”

See related GNN article
»Mapping the Horse

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Chowdhary, B.P. et al. The first-generation whole-genome radiation hybrid map in the horse identifies conserved segments in human and mouse genomes. Genome Res. 13, 742-751 (April 2003).

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