Genetic Diversity And Maternal Origin Of Chinese Domestic Horses

All 182 mtDNA D-loop 247bp sequences of 9 Chinese domestic horse breeds were analyzed to detect their genetic diversity and origin by using PCR and bioinformation technology. These horse breeds includes Ningqiang horse, Kazak horse, Guizhou horse, Guanzhong horse, Mongolia horse, Tibet horse, Guanshan horse, Yunnan horse and Guangxi horse. The main results in this study are as follows:(1) Among all 182 sequences of 9 domestic horse breeds,the average nucleotide content are: 29.7% for T, 26.6% for C, 31.8% for A and 11.9% for G. Average (A+T) content is 61.5% and 38.5% for (G+C), the former is apparently higher than the latter, it is suggesting that the base bias which is in proportion to mammalian mitochondrial DNA nucleotide composition.(2) All 182 sequences defined 70 different haplotypes with 47 variable sites. 47 sites are with 19.03% of 247 bp D-loop region, 43 of these sites are transitions, 2 of them are transvertions, 2 of these sites have both transitions and transvertions.(3) There is high level of genetic diversity in Chinese domestic horses. The haplotype diversity and the nucleotide diversity were 0.842~0.994 and 0.0219~0.0293 respectively, of which Guanzhong horse displayed the lowest level, while Mongolia horse held the highest. The mean haplotype diversity and the mean nucleotide diversity in all breeds were 0.946 and 0.0247.(4) NJ phylogenetic analysis in Chinese horse mtDNA suggested that Chinese domestic horse revealed seven maternal origins (A-G), 17 sublineages,showing multiple maternal origins.(5) Nine ancient DNA sequences were compared with 70 haplotypes from Chinese native horses. The NJ tree showed that the 9 ancient DNA sequences shared 7 haplotypes which were quite similar to modern day equine mtDNA, clustered in haplogroups A, E, and F. This result also suggested that horses of prehistoric Mongolian plateau probably had multiple origins. The modern and ancient mtDNA sequences presented here support the currently accepted hypothesis of multiple origins in horses.