Polymorphism study of growth differentiation factor 9B (GDF9B) gene and its association with reproductive traits in sheep

GDF9B protein plays a critical role in growth and differentiation of early ovarian follicles. In Inverdale and Hanna sheep, mutations in exon-2 of GDF9B gene have been recorded to show increased ovulation rate in heterozygous condition whereas homozygotes are infertile. Present screen study was carried out to explore the presence of these reported mutations in Corriedale and Local Kashmir Valley sheep with high rate of twinning. Exon-2 of GDF9B gene was amplified and the polymorphism was explored by SSCP technique. In the process three different bandings were observed. Later on these patterns corresponded with three different allelic forms on nucleotide sequencing. Phylogenetic analysis revealed that the nucleotide sequences of alleles observed in the present study and that of a published sequence of sheep were having the same point of origin. The results were also compared with goats, large ruminants and humans. The allelic frequencies of allele A and B were 0.64 and 0.36, respectively in Corriedale sheep whereas the allelic frequencies of all the three alleles in Kashmir Valley sheep were 0.60, 0.34 and 0.06. SNP “C” of the designated genotype AC was observed to pronounce a significant effect on litter size with average litter size going up by 0.63 as compared with the nearest genotype AB wherein the litter size was 1.29±0.05. The average litter size between AA and AB genotypes did not vary significantly. ► GDF9B gene in sheep under study was observed to be polymorphic. ► Three different alleles identified by SSCP were confirmed by nucleotide sequencing. ► Two new mutations resulted in replacement of asparagine and methionine amino acids. ► The identified mutation seems to pronounce significant effect on litter size. ► The mutations observed herein lie in the reported “mutational hotspot” of the gene.