Association between PCR-SSCP of growth differentiation factor 9 gene and high prolificacy in Small Tail Han sheep

Small Tail Han sheep that has significant characteristics of high prolificacy and nonseasonal ovulatory activity is an excellent local sheep breed in P.R. China. The lambing percentage averaged 260% in Small Tail Han sheep. Growth differentiation factor 9 (GDF9) gene, which was essential for growth and differentiation of early ovarian follicles, was considered as a possible candidate gene for litter size in Small Tail Han sheep. The genetic polymorphism of a part of the GDF9 gene was detected in 130 ewes of Small Tail Han sheep by PCR-SSCP. The results indicated that there were two genotypes (AA and AB) detected by two primer pairs. In both exon 1 and exon 2 of the GDF9 gene in Small Tail Han sheep, frequencies of AA genotype were 0.846 and 0.908, frequencies of AB genotype were 0.154 and 0.092, frequencies of A allele were 0.923 and 0.954, and frequencies of B allele were 0.077 and 0.046, respectively. The results of chi2 fitness test indicated that both exon 1 and exon 2 of the GDF9 gene were in Hardy-Weinberg equilibrium (p > 0.05) in Small Tail Han sheep. Least squares means of litter size in the first and the second parity for genotype AA were 0.30 (p <0.05) and 0.77 (p <0.0001) more than those for genotype AB detected in exon 1 of the GDF9 gene in Small Tail Han sheep, respectively. Fragments detected in exon 2 of the GDF9 gene had no significant effect (p > 0.05) on litter size in both the first and the second parity in Small Tail Han sheep. Litter size in sheep is lowly heritable, expressed only in females, and manifested relatively late in life. Access to genetic markers would thus be advantageous in selection programs.