[Polymorphisms of exon 2 of MHC-DRB3 gene in Mongolian and Kazakh Sheep].

MHC(major histocompatibility complex) is a chromosomal region consisting of a group of closely linked loci which are highly polymorphic, which plays a central role in the immune system of animals and is almost found in all vertebrates. Its expressional product is MHC antigen of which main function is antigen presentation. In this study, the exon 2 of MHC-DRB3 gene was amplified by PCR and a uniform fragment of 285 bp was obtained in Mongolian Sheep and Kazakh Sheep. The 285 bp PCR product was digested with restriction endomuclease HaeIII and genetic polymorphism was investigated by PCR-RFLP. Seven alleles were found: A(168 bp/117 bp), B(154 bp/117 bp/14 bp), C(154 bp/65 bp/52 bp/14 bp), D(168 bp/65 bp/52 bp), E(154 bp/131 bp), F(154 bp/66 bp/65 bp), H(220 bp/65 bp). There are seventeen genotypes in the tested populations, BB(154 bp/117 bp/14 bp), CC(154 bp/65 bp/52 bp/14 bp), EE(154 bp/131 bp), HH(220 bp/65 bp), FF(154 bp/66 bp/65 bp), AB(168 bp/154 bp/117 bp/14 bp), AC(168 bp/154 bp/117 bp/65 bp/52 bp/14 bp), AE(168 bp/154 bp/131 bp/117 bp), AH(220 bp/168 bp/117 bp/65 bp), BC(154 bp/117 bp/65 bp/52 bp/14 bp), CE(154 bp/131 bp/65 bp/52 bp/14 bp), CD(168 bp/154 bp/65 bp/52 bp/14 bp), CF(154 bp/66 bp/65 bp/52 bp/14 bp), CH(220 bp/154 bp/65 bp/52 bp/14 bp), DE(168 bp/154 bp/131 bp/65 bp/52 bp), EH(220 bp/154 bp/131 bp/65 bp), FH(220 bp/154 bp/66 bp/65 bp). By analyzing restriction map, polymorphic sites were detected at base position 154, 168 and 220. Statistical results indicated that there are significant differences of some genotypic frequencies and allelic frequencies between Mongolian Sheep and Kazakh Sheep(P < 0.10, P < 0.05 or P < 0.01). CC, FF, BC and B, C, F are favorable genotypes and favorable alleles respectively in Mongolian Sheep and Kazakh Sheep, In addition, HaeIII CE and HaeIII E is favorable genotype and favorable allele respectively in Kazakh Sheep. The results of chi 2 test showed that genotypes of MHC-DRB, gene in Mongolian Sheep and Kazakh Sheep did not fit with Hardy-Weinberg equilibrium(P < 0.01).