What makes one Shetland shorter or taller than another? Swiss researchers say there’s at least one gene they can identify as a “wither height” gene in these ponies.

A gene called HMGA2 found on equine chromosome 6 appears to be responsible for Shetland wither height, said Mirjam Frischknecht, PhD, of the Institute of Genetics, Vetsuisse Faculty of the University of Bern, and the Agroscope, Swiss National Stud Farm, in Avenches. Frischknecht presented her study at the 10th annual Swiss Equine Research Day held April 19 in Avenches.

Researchers know that HMGA2 has a link to height in other mammalian species, including humans, Frischknecht said. So she and her colleagues decided to explore the genotypes of 48 Shetland ponies ranging in height from 70 to 107 centimeters (27.5 to 42 inches). By comparing genome analysis results with the ponies’ body heights, the researchers detected an association between HMGA2 and wither height.

Then, the researchers carried out fine mapping of causative variants (gene variations suspected to be responsible for detectable difference—in this case, height differences) through full genetic sequencing of two ponies. These two ponies were at extreme ends of the height scale: One was 70 centimeters tall, and the other stood 106 centimeters