Genetic Resource Characters Of Southwest Horse Populations In China

Chinese Southwest horse distributes throughout the Southwestern region of China, and is one of the most important composition of Chinese horses owing to their large number and abundant breed types. During undergoing genetic variation and natural selection of a long-term evolutionary course, the different typed populations have been gradually differentiated, such as Baise horse, Guizhou horse, Wenshan horse, Wumeng horse, Dali horse, Jianchang horse, Tengchong horse and Zhongdian horse, and so on. Chinese Southwest horse populations are one of the original and natural pony breeds in the resource pool of China and even the world. Chinese southwest horse is valuable genetic resources of human being because of some good qualities including dwarf somatotype, compact structure, strong stress resistance and being good at walking rugged mountain road. So can be used as materials or tools of scientific research, sightseeing, artistic performance, ridding training, and transportation. In view of this, Chinese southwest horse type populations own important statuses for protective utilization of genetic resource. The profundity of research work was few about Chinese southwest horse's genetic diversity, origin evolution, genetic relationship, resources distribution, and the mechanism of dwarfishness. Based on a preliminary investigation for southwest region of China, including seven local breeds and a foreign variety, Shetland, totaled 150 samples, we detected the polymorphisms of D-Loop region, ND3, ND4, ND4L on mitochondrial DNA and SHOX on nuclear DNA by PCR-SSCP, sequencing, and other methods, and analyzed the resource characteristics of South-west horse by using SAS, SPSS statistical analysis software. And we conducted a correlation analysis between polymorphisms and body measurements, further understanding the colony resource's phenotypic and molecular characteristics of Chinese southwest horse populations, the basic conclusions were followed:(1) Considering the amount of Chinese southwest horse as it stands, it has become the largest group in the five main groups in China. The main factors of influencing the abundance distribution were: agricultural machinery per capita, population density, administrative district ratio, and so on. The density-independent factors were taken into account and annual frost-free period, precipitation, sunshine hours, the average temperature have powerful effect for Chinese southwest horses and they might play a leading role in the formation of different Chinese southwest horse types. (2) The mtDNA D-Loop of Chinese southwest horses were detected and sequenced. The results showed that there is relatively abundant genetic diversity in Chinese southwest horse populations and the he genetic differentiation of Chinese southwest horse within the types and among the types is not significant (P>0.05). And more Chinese southwest horse came of multiple female ancestors, close genetic relationship with Mongolian horse of Mongolia, and several South-west horse populations originated from Przewalskii horse, namely Mongolian wild horse.(3) Polymorphisms in ND4L, upstream and downstream of ND4 gene were detected: ND4L and upstream of the ND4 fragment both exist two haplotypes (defined as A and B), and the frequency of B haplotype were slightly higher than the A haplotype; in the downstream of ND4 fragments, there are four haplotypes, and one is shared haplotype, the others are rare ones.(4) The bias of nucleotide composition of ND4 and ND4L genes in South-west horse is not critical, but on the sites of the second and third codons, the content of C is far greater than the content of G, and found bias exist in the usage of the codons.(5) Nucleotide diversity (Pi) of six groups(excluding Jianchang horse) within Chinese southwest horse alternates from 0.00467 to 0.00737, and the results showed abundant polymorphism appeared inter-groups. Genetic distance is lower among all types, and the genetic distance between Wumeng horse and the others are the greatest (0.006). The Index of Nucleotide Differentiation (Nst) among six groups varies between -0.35665 to 0.01694 and Nst of Wumeng horse and other groups are all relatively big. The Nst between Wumeng and Dali horse is the largest one, despite in the same district, therefore genetic differentiation exists between Wumeng horse and Dali horse.(6) The correlation analysis between the polymorphisms of ND4 downstream fragment and body size showed that the genotype had significant impact on body length (P <0.05): the effect of genotype D is the largest one among all the genotype effects; the impacts of genotype on height and cannon circumference were close to a significant level (P = 0.0809 and 0.0753), the chest circumference was not significantly affected.(7) Chinese southwest horse showed low genetic diversity, close genetic distance, and high genetic similarity within groups. The independence of Wu Meng horse is the highest (Pi=0.00737) one, so can be tackled as an independent management unit; nucleotide diversity of Dali horse is minimum (Pi=0.00467), and the coefficient of division is smallest (k= 3.167), maintained as a unique group of genetic specialty, so it should be well protected. (8 In the paper, we cloned a partial sequence of the SHOX gene about dwarfism trait of pony for the first time. The length of the sequence is 520bp. After aligning, showed that the sequence we acquired is partial CDS of SHOX gene, including the complete the second exon.(9) By aligning with other species on the homologous sequence of the second exon of SHOX gene, we discovered that the second exon is more conservative among different species, no Indels(insertion and deletion) and STRs(short tandem repeat) were found in the region, and the SHOX gene of horse is GC-rich (the average value of seven groups is 67.85%).(10) Detecting the variations in the SHOX gene via PCR-SSCP, we found in the P2 locus of 268 existed a G→A transition, and at 431 was a T→G transversion, resulting in the B allele into allele A.(11) The analysis of SHOX gene P2 locus about the gene heterozygosity(He), the gene homogeneity index(Ho), the number of effective allele(Ne), and polymorphic information content (PIC) showed that: the value of PIC of Yunnan Wenshan horse is significant than the others, and it is 0.513, in a high polymorphic degree; Sheteland horses were the lowest, only is 0.222.