Allelic polymorphism in exon 1 of GDF9 and exon 2 of BMP15 genes and its impact on litter size at lambing in Iran-Black sheep

The main purpose of this study was to assess the presence of the previously reported single nucleotide polymorphisms (SNPs) in the sheep growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) genes and their association with litter size at lambing in Iran-Black sheep breed. Blood samples were taken from 120 Iran-Black ewes. DNA extraction was conducted using a modified salting-out method. DNA fragments with sizes of 462bp and 141bp for the GDF9 and BMP15 genes were amplified using PCR with specific primers, respectively. The PCR-RFLP approach was adopted for detecting the genotypes. The results indicated that the SNP in the exon 2 of BMP15 is a monomorphic locus in Iran-Black sheep. However, the substitution of G to A nucleotide was determined in the GDF9 locus. Digestion of the 462bp PCR product from exon 1 of the GDF9 using the HhaI restriction enzyme produced fragments of 52, 156, and 254bp. However, DNA fragments containing the A nucleotide yielded only two fragments (52 and 410bp). The heterozygous animals for this mutation in GDF9 locus had fragments of all four sizes (52, 156, 254, and 410bp). The frequency (0.75) of the wild type allele (+) in GDF9 locus was higher than the frequency (0.25) of mutant allele (G). The observed frequencies for the GG, G+ and ++ genotypes were 0.05, 0.40 and 0.55, respectively. The association results indicated that the mutation of GDF9 gene has a substantial impact on lambing rate and the Iran-Black ewes with the GG and G+ genotypes had higher lambing rate than those with the ++ genotype. Thus, a gene assisted selection program to improve lambing rate in this breed can be designed based on the GDF9 gene mutation.