Evaluation of BMP2 Gene Exon 1 Polymorphism and its Effect on Weight of Tail in Fat-tailed Lori Bakhtiari Sheep

Having a fat tail is a characteristic of some Iranian native sheep breeds, whose main role is usually to store energy for using in limited food conditions. However, the amount of energy required to store fat in this tissue directly affects the efficiency of meat production and carcass quality. In Iran, the average weight of each carcass is about 15.3 kg, of which 15% is the fat tail. It requires 1.7 kg more feed per kilogram of fat tail than meat (protein), and customers pay a lower price per unit of weight for sheep with heavier fat tail. Today, researchers in the field of animal breeding have a special focus on reducing the weight of the fat tail and increasing the marketability of sheep carcasses. Bone morphogenetic protein 2 (BMP2) belongs to the β-metamorphic growth factor of the β family and plays an important role in bone and cartilage development and, therefore, seems to be the best candidate for the fat-tailed phenotype. Comparison of the results of genotype obtained from Ovine SNP50K Bead Chip in tow fat-tailed breeds with the results obtained in 13 thin tail breeds showed a missense mutation in BMP2 gene, with the frequency of different alleles in these two different groups. In this study, in order to detect the polymorphism in BMP2 gene exon 1 and investigation of its relationship with tail fat trait, blood samples from 150 same age ewes of Lori Bakhtiari breed were randomly taken which are maintained in Gahar Dorud sheep breeding center (Dorud, Lorestan). DNA extraction was performed using a special DNA extraction kit (Pars Toos, Iran) according to the manufacturer's instructions. Determination of quality and quantity of extracted DNA was performed using agarose gel electrophoresis and nanodrop spectrophotometer, respectively. BMP2 gene exon 1 was amplified successfully by a pair of specific primer. The accuracy of this process was confirmed by 1.5% agarose gel. Then, using PCR-SSCP technique, 12% polyacrylamide gel and silver nitrate staining, probable polymorphisms were tracked in this position and finally calculation of Chi-square test (χ2) for deviation from Hardy-Weinberg equilibrium (HWE) has been assessed by Popgen (Ver. 1.32) software. The relationship between genotypes and average fat tail weight (Corrected by body weight (BW)) has been analyzed with the PROC GLM procedures in Statistical Analysis System (SAS) v. 9.1 version. Based on the results, amplification of BMP2 gene exon 1 was successfully done and three different patterns of polymorphism have been detected through SSCP analysis.  Exon 1 of BMP2 gene in Lori Bakhtiari ewes containing A and B alleles with distributions of 197 and 103 and frequency of 65.7% and 34.33%, respectively, that have generated AA, AB and BB genotypes with distribution of 75, 47 and 28 and frequencies of 50%, 31.33% and 18.67%, respectively. Mean comparison of fat tail weight in each genotype using Duncan procedure showed that the effect of genotype on fat tail weight in Lori Bakhtiari breed was significant (P <0.05). AA genotype with average fat tail weight of 5.16 showed higher performance than AB genotype with average fat tail weight of 4.29 and BB genotype with average fat tail weight of 3.76. The results of statistical analysis also showed that the presence of allele A causes heavier fat tail weight and the presence of B allele causes lower fat tail weight (P <0.05). Heterozygosity and Homozygosity observed in this study are 0.3154 and 0.6846, respectively. The significance of the calculated chi-square genotypic frequency in each population at the level of 0.05 in comparison with the chi-square table shows that the studied populations are not in Hardy-Weinberg equilibrium. Which can be attributed to the pressure of selecting on reference population for genetic breeding for fat tail weight at Gahar Dorud sheep breeding center. Today, advances in genomic technologies have multiplied, and if information on loci associated with meat quality traits can be obtained and the genes that control these traits are located on chromosomal sites, they can be incorporated into breeding programs. Breeds should be used with MAS and cause genetic growth and development of these traits. Using molecular detection methods and identifying sheep carrying B alleles and selecting them as the parents of the next generation, we can move towards producing herds with lower fat tail weight and more marketability.