What makes your horse different from the horse in the next stall? Why doesn’t a Kentucky Derby contender walk like a Budweiser Clydesdale? Why don’t either of them look like Thumbelina, the Guinness Book of World Records’ smallest living horse?

The domestic horse comes in a range of sizes, shapes, and temperaments–from the tiny American Miniature Horse to the massive draft breeds, humans have historically bred horses for both aesthetic and functional qualities. For the horse in particular, size and conformation have been two major driving forces for the development of the diverse breeds we see today. Horses have been bred to pull carts, jump fences, or run a mile-long race. When horse breeders look to improve these abilities in their stock, they are often selecting for changes in genes, called alleles, that affect body size and conformation.

Allele variation in several genes has already been shown to contribute to body size diversity in many species. As body size genes affect fundamental developmental processes such as cell growth, they can sometimes be correlated to other diseases, like the tumor growth seen in cancer. By exploring the genetics of body size in the horse, researchers at Cornell University aim to improve not only the livelihood of the horse population, but also better understand the genetics of diseases that affect all mammals, including humans. Furthermore, when they investigate body size genes, they will look for genes that contribute to breed-specific traits in the horse, especially the conformation and skeletal qualities valued by breeders