Genetic diversity of Cheju horses (Equus caballus) determined by using mitochondrial DNA D-loop polymorphism.

We used sequence polymorphism of the mitochondrial DNA D-loop (968 bp excluding the tandem repeat region) to determine genetic diversity of horses inhabiting Cheju (a southern island of Korea). Seventeen haplotypes with frequencies from 1.5 to 21.5% were found among 65 Cheju horse samples. Genetic diversity (h) of the 17 haplotypes was calculated to be 0.91, indicating that the extant Cheju horse population consists of diverse genetic groups in their maternal lineage. Phylogenetic analysis showed that 17 types of Cheju (D-loop sequences determined), 5 Mongolian, 6 Arabian, 3 Belgian, 2 Tsushima, 2 Yunnan, 1 Przewalskii, and 3 Thoroughbred horses (published sequences for the latter seven breeds) showed that Cheju horses were distributed into many different clusters in the tree. Four Mongolian horses clustered with separate Cheju horse groups, showing that some Cheju horses are clearly of Mongolian origin. The analysis of partial sequences (284 bp) of the D-loop of 109 horses showed that Thoroughbred, Mongolian, Lipizzan, and Arabian breeds are as diverse as Cheju horses. Our data together with others suggest that most horse breeds tested with reasonably sufficient numbers of samples are diverse in their maternal lineages and also are not uniquely different from each other.