بررسي ساختار ژنتيكي و روابط فيلوژني اسب هاي كاسپين، عرب و تالشي

Investigation of the genetic structure and phylogenic relationships of Caspian, Arabic and Taleshi horses

نژادهاي بومي به دليل داراي بودن ويژگي­هاي منحصر به فرد، جزء ذخاير ژنتيكي كشور محسوب شده و شناخت بيشتر ساختار ژنتيكي آنها به حفظ و حراست آنها و تدوين برنامه­هاي اصلاح نژادي كمك خواهد كرد. در اين پژوهش تنوع ژنتيكي 136 رأس اسب از سه نژاد ايراني (كاسپين، عرب و تالشي) با استفاده از 12 نشانگر ريزماهواره توصيه شده توسط انجمن بين المللي ژنتيك حيواني، مورد بررسي قرار گرفت. تمام نشانگرهاي استفاده شده چند شكل بودند و نشانگرهاي ASB17 با 12 آلل و HMS6 با 6 آلل به ترتيب بيشترين و كمترين تعداد آلل را توليد كردند. بيشترين و كمترين ميزان هتروزيگوسيتي مورد انتظار به ترتيب در نشانگرهاي VHL20 (0/78 و (ASB23 (0/62 محاسبه شد. ميانگين شاخص شانون براي همه جايگاه­ها برابر با 1/72 به دست آمد. در نمودار فيلوژني رسم شده با استفاده از ضريب تشابه جاكارد و روش (UPGMA (14، اسب­ هاي كاسپين و تالشي در يك شاخه و اسب­هاي عرب در شاخه جداگانه قرار گرفت. آناليز واريانس مولكولي نشان داد كه تنوع ژنتيكي زيادي در درون نژادهاي بررسي شده وجود دارد و با توجه به جمعيت كم اسب­هاي تالشي و كاسپين، پيشنهاد مي ­شود برنامه­ هاي اصلاح نژادي جهت بهبود كارايي و جلوگيري از انقراض آنها تا رسيدن به سطح امن طراحي و اجرا گردد.

Introduction2Due to having historical value and climatic diverse, Iran has unique horse breeds. Unfortunately, due to the lack of attention and control of the import of foreign breeds into this rich genetic source, huge damage has been created. Therefore, many horse breeds in the country got crossbred and their racial purity reduced. Knowing the genetic structure of native breeds will play an important role in their safeguarding and ensuring of their survival. Indigenous breeds, due to their unique characteristics, are considered as part of the genetic resources of the country, and their genetic structure will help them to protect and develop eugenic programs. Materials and Methods This study was conducted on 136 horses including Taleshi (25 samples), Caspian (49 samples) and Arabic (62 samples) breeds from their breeding areas. Taleshi horse samples was captured from local stock in the Guilan province, Caspian samples was captured from horse riding clubs around Tehran and Guilan provinces, and Arabian samples was captured from horse riding clubs around the provinces of Tehran, Khuzestan and Alborz. They were unrelated and selected randomly. The race recognition of horses was based on books published by the Federation of Equestrian and their phenotypic characteristics. After determining of the concentration and uniformity of the concentration of extracted DNA, all individuals under study were conducted for 12 microsatellite markers recommended by the Animal Genetic Association (ISAG) to determine the genotype in order to estimate the parameters such as heterozygosity, inbreeding, Hardy and Weinberg equilibrium, and so on and find an appropriate strategy to maintain these valuable breeds. The number of observed alleles (na), and effective (ne), observed heterozygosity (Ho) and the Expectation case (He), Shannon index (I), inbreeding coefficient (ISF), genetic distance, genetic similarity, Hardy-Weinberg equilibrium, and phylogeny tree between races were calculated using POPGENE 1.31 software. Results and Discussion All of the used markers were multi-shaped and the ASB17 markers with 12 alleles and HMS6 produced the highest and lowest number of alleles with 6 alleles, respectively. The highest and lowest expected heterozygosity were calculated in VHL20 (0.78) and ASB23 (0.62) markers, and the average Shannon index for all sites was 1.72. Hardy Weinberg balance analysis by Chi square test showed that except ASB2 and HMS3 markers in Taleshi breed, ASB17 and HTG4 markers in the Caspian breed and ASB17 markers in the Arabic breed, all markers had a significant deviation from Hardy and Weinberg equilibrium (P <0.05). The highest observed heterozygosity was related to AHT5 marker (0.81) and the lowest observed heterozygote was related to ASB17 and HTG4 markers (0.68). The Shannon index, like the observed heterozygosity, shows the amount of genetic diversity, and because the maximum value is equal to Ln (n), it is useful to express the genetic diversity of multi-formed sites. The highest and lowest values of Shannon index were 1.96 and 1.46, respectively, for VHL20 and HTG4 markers. Given the fact that the VHL20 marker showed the highest and the HTG4 marker showed the least effective allele, so the calculated values for the Shannon index are justified. Phylogeny diagram showed that Caspian and Taleshi horses were placed in one branch and Arab horses in separate branch. Conclusion Breeds with fewer populations are more at risk for genetic changes and extinction. Reducing of the genetic diversity of indigenous populations will result in the loss of many useful genes, especially those that are compatible with different environments and resistant to regional diseases. Undoubtedly, it is very important to pay attention to the genetic diversity of small-sized population of breeds such as Taleshi and Caspian. The results of this study showed that due to the low number of Caspian and Taleshi horses, genetic diversity is still at a high level, so it would be hoped that by adopting the principled measures, we would prevent their extinction in the long duration.