Breed Differences in Dopamine Receptor D4 Gene (DRD4) in Horses.
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.
Department of Psychology, Graduate School of Letters, Kyoto University, Sakyo, Kyoto 606-8501, Japan ; Japan Society for the Promotion of Science, Chiyoda-ku, Tokyo 102-0083, Japan.
Yusuke
Y
Hori
Faculty of Applied Biological Sciences, Gifu University, Gifu 501-1193, Japan.
Takatoshi
T
Ozaki
Hokusho Agricultural High School, Hirado, Nagasaki 859-4824, Japan.
Yoshimitsu
Y
Yamada
Laboratory of Racing Chemistry, Utsunomiya, Tochigi 320-0851, Japan.
Teruaki
T
Tozaki
Department of Biological Sciences, College of Natural Sciences, Pusan National University, Pusan 609-735, Korea.
Heui-Soo
HS
Kim
Department of Psychology, Graduate School of Letters, Kyoto University, Sakyo, Kyoto 606-8501, Japan ; Japan Society for the Promotion of Science, Chiyoda-ku, Tokyo 102-0083, Japan.
Ayaka
A
Takimoto
Animal Resource Science Center, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Kasama, Ibaraki 319-0206, Japan.
Maiko
M
Endo
Animal Resource Science Center, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Kasama, Ibaraki 319-0206, Japan.
Noboru
N
Manabe
Wildlife Research Center, Kyoto University, Sakyo, Kyoto 606-8203, Japan.
Miho
M
Inoue-Murayama
Department of Psychology, Graduate School of Letters, Kyoto University, Sakyo, Kyoto 606-8501, Japan.
Kazuo
K
Fujita
SNP; behavioral trait; breed difference; dopamine receptor D4 gene; native Japanese horse