It’s time for some stereotyping: How would you describe the personality of a Thoroughbred? How about an Arab? Shetland pony? Appaloosa? Belgian Draft? Native working horses in Africa and Asia? If you think you can make some generalizations about breed personalities, scientists say you could be right.

Results from recent studies by a Japanese research group suggest there’s biologic evidence that a horse’s personality is based on his genes, and that these genes differ from one breed to another. What’s more, the researchers are even honing in on exactly where certain personality traits can be found on different breeds’ genomes.

The key is dopamine—a natural chemical in the nervous system—which appears to play an important role in how horses behave socially and develop personality, said Yusuke Hori, PhD candidate, researcher in the department of psychology at Kyoto University in Kyoto and at the Japan Society for the Promotion of Science in Tokyo.

Specifically, one particular dopamine receptor—the “D4″ receptor (or DRD4), as scientists call it—has been previously shown to affect equine personality. So Hori and his fellow researchers set out to find the D4 gene in a variety of horses and then compare their findings across different breeds