| Yaks belong to the genus Bos, the family Bovidae, the order Artiodactyla, and the class Mammalia. Yak’s karyotype is 2n=60. The genomic DNA sequences available from GenBank are 2,645.15 Mb. In this study, the characteristics of microsatellite sequences were retrieved and analyzed based on the released DNA sequences available from GenBank. Then the rapid screening of Maiwa yak’s microsatellite loci was performed by PCR amplification. The genetic diversity and population structure of Maiwa yak sampled from Hongyuan county of Sichuan province was studied after the microsatellite loci had been successfully screened. The main results were as follows:The characteristic analysis of microsatellites in Bos mutus’s genomeIn the length of 251540707 bp retrieved, which was only 9.51% of yak’s whole genome,43409 microsatellite loci has been found. According to the structural analysis, we found that the each number of perfect, imperfect and compound microsatellite loci was 42063,1009 and 411, with the percentage of each was 96.734%,2.320% and 0.945%, respectively. These microsatellites could also be divided into di-nucleotide, tri-nucleotide, quart-nucleotide, quint-nucleotide and sex-nucleotide based on repeat unit. The majority of these repeat units was quint-nucleotide microsatellite (16787), with the percentage of 38.59%. Then the gross and percentage of di-nucleotide, tri-nucleotide, quart-nucleotide and sex-nucleotide microsatellite was 12377 (28.45%), 9466 (21.76%),3855 (8.86%) and 1013 (2.33%), respectively. A detailed analysis of perfect microsatellite loci showed that, AC (AC/CA/TG/GT), AGC (TCG), AAAT (TTTA), ACTGA (TGACT) and TGAAAG (ACTTTC) was the majority repeat of di-nucleotide, tri-nucleotide, quart-nucleotide, quint-nucleotide and sex-nucleotide microsatellites, respectively, with the percentage of each was 60.15%, 31.04%,18.36%,19.36%and 11.05%, respectively.The screening and verification of microsatellite loci based on the genomic DNA of Maiwa yakIn this study, the microsatellite loci of Maiwa yak were screened by PCR amplification of the genomic DNA of Maiwa yak. Primers were designed on the flanking sequence of microsatellite loci. Although 470 pairs of primers were synthesized while a large number of them were designed, only 77 microsatellite loci were screened and amplified successfully by using Maiwa yak genome as a temple, which contained 35 di-nucleotide microsatellite loci,15 tri-nucleotide microsatellite loci,15 quart-nucleotide microsatellite loci and 12 quint-nucleotide microsatellite loci. The success rates of screening are 46.1%,31.9%, 33.3% and 30%, respectively. The result of sequencing verified the reliability of the experiment.The genetic diversity of microsatellite loci and population structure of Maiwa yakSeventy seven microsatellite loci were amplified by using genomic DNA of 191 Maiwa yak individuals. The polymorphic microsatellite loci were genotyped through polyacrylamide electrophoresis experiment or capillary electrophoresis experiment. The data were recorded and the polymorphism of each microsatellite locus was analyzed through Cervus3.0 and Genepop4.2 software. Consequently, the structure characteristics of Maiwa yak population was studyed by Structure 3.0 programme. The average number (N) of di-nucleotide, tri-nucleotide, quart-nucleotide and quint-nucleotide microsatellite allele was 10.943,9.267,4.2 and 2.75, respectively. The average observed heterozygosity (Ho) was 0.7346,0.5041,0.4191 and 0.3830, respectively. The average expected heterozygosity (He) was 0.7921, 0.8152,0.5814 and 0.4501, respectively. The average polymorphism information content (PIC) was 0.7617,0.7831,0.5130 and 0.3652, respectively. Most of the microsatellite loci (40 microsatellite loci) existed higher polymorphism (PIC>0.5). Twenty eight microsatellite loci exhibited higher polymorphisms (0.25<PIC<0.5). Only three ones existed low polymorphisms (PIC<0.25). Three polymorphisms index (Ho, He and PIC) were strong negative correlation (Ho:r=-0.931; He: r=-0.930; PIC:r=-0.933) with the length of the repeat unit in correlation analysis, which reached extremely significant level (P< 0.01). The population of Maiwa yak showed monomorphic structure in the genetic differentiation analysis, which suggested that Maiwa yak polulation in this study were lack of artificial selection breeding in a relatively isolated geographical environment and long-term grazing feeding. All these results indicated that Maiwa yak was a breed of higher purity and possessed the basic qualifications to be preserved as an excellent local breed. |
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