Polymorphisms Of The Gene ELA-DRA *exon2 In Przewalski's Horse And Two Kinds Of Xinjiang Local Breeds

Przewalski's horse is considered as the only survived wild horse species in the world and they were listed in the First Category of State Key Protected Wildlife List. Przewalski's horses were originated from arid desert grassland areas of Dzungaria basin in Xinjiang, China and Mongolia, so they are also called Dzungarian wild horse or Mongolian wild horse. The Przewalski's horse is extinct in the wild by the middle of last century and all the living individuals descend from 12 founders.In the mean time, Domestic horses in Xinjiang experienced long evolutionary process of genetic variation and natural selection, and gradually differentiated into select horse breeds such as Hasak horse, Yanqi horse. The native horse breeds in Xinjiang pocess excellent qualities as anti-cold, rough feeding tolerance, good adaptability. In this study, the genetic polymorphisms and allele-frequency distribution of three horse breeds investigated for exon2 of MHC-DRA by PCR-SSCP and sequencing,it would provide important experiment gist in order to posting ELA(Equine Leukocyte Antigen)genetic characteristics.The result showes that:1. Seven kinds of genetypes were detected in three types of horses by using PCR-SSCP techniques.They were named AA,BB,CC,AB,AC,BC and AD respectively.Five genetypes were found in Hasak horse and Yanqi horse,but only three genetypes were found in Przewalski's horse. These horses all have AC. AA genetypes is dominant genotype in Hasak horse and Yanqi horse. CC is the dominant genetype in Equus przewalskii.2. The results of allele frequencies showed that A is the dominant allele in Hasak horse and Yanqi horse,the frequencies were 0.734 and 0.71 respectively. C is the dominant genetype in Equus przewalskii,but allele D is only found in Yanqi horse. The disequilibrium of allele frequency in this three types horses implied that genetic management should focus on low frequency alleles to preserve genetic diversity at maximum extent.3. The analysis of PIC and He showed that the three horse types belonged to intermediate polymorphism. The values of PIC and He in Equus przewalskii are lower than Kazakh horse and Yanqi horse. It illuminate Equus przewalskii are inferior to the Kazakh horse and Yanqi horse in resistance to diseases and adaptability.4. The phylogenetic tree and genetic distance of populations based on ELA-DRA sequences show that the phylogenetic relationship between Hasak and Yanqi breeds were very close. The phylogenetic relationship between Equus przewalskii and two kinds of local breeds were far. The phylogenetic relationship between Equus przewalskii and Hasak horse were farthest.5. The molecular tree was designed using the neighbour joining method with Kimura-2 parameters correction. Analysis of evolutionary trees showed that the domestic horse DRA alleles were separated from the zebra group, the horse alleles were closer to the root of the tree with a single exception (ELA-DRA*JBH11). On the other hand, the ass/donkey DRA sequences clustered with all other species.