| Abstract: | Genetic polymorphisms in genes related to neurotransmitters or hormones affect
personality or behavioral traits in many animal species including humans. In domestic
animals, the allele frequency of such genes has been reported to be different among breeds
and it may account for breed differences in behavior. In this study, we investigated breed
differences in horses in the dopamine receptor D4 gene (DRD4), which has been reported to
affect horse personality. We collected samples from seven horse breeds including those
native to Japan and Korea, and compared the sequence of the DRD4 exon3 region among these
breeds. We found that there were two types of polymorphisms (VNTR and SNPs) in the exon3
region, and some of them seemed to be breed-specific. In addition, we found that the
allele frequency of G292A, reported to be associated with horse personality, differed
greatly between native Japanese horses and Thoroughbred horses. The frequency of the A
allele which is associated with low curiosity and high vigilance, was much lower in native
Japanese horses (Hokkaido, 0.03; Taishu, 0.08) than in Thoroughbreds (0.62). This
difference may account for breed differences in personality or behavioral traits. Further
studies of the function of these polymorphisms and their effect on behavior are
indicated. |
