Polymorphisms of the , and fecundity genes in four Chinese sheep breeds.

Numerous studies on prolific sheep breeds have shown that the transforming growth factor beta (TGF- ) superfamily members, including bone morphogenetic protein receptor type 1B (), bone morphogenetic protein 15 () and growth differentiation factor 9 (), are the essential regulators of ovulation rate and litter size. In total, 11 known mutations (1 in , 6 in and 4 in ) are able to increase the ovulation rate and litter size, respectively. In this study, the genomic DNA was isolated from 512 high-prolificacy sheep (including the Small-tailed Han, Hu and Wadi sheep breeds) and 164 low-prolificacy sheep (Tan sheep), and genotyping of the specific mutations of the three fecundity-related genes was carried out by sequencing. The results showed that the mutation in was detected in all four sheep breeds, and the frequency of B allele was significantly higher in the high-prolificacy breeds than that in the low-prolificacy breed ( ). A novel mutation, c.T755C (named S1), was found in from the four sheep breeds. However, known mutations such as , , , , and were not detected in these breeds. Three known loci (G1, G3 and G4) and a new mutation, c.A1515G (named S2), were found in , and the other three known mutations ( (G8), and ) were not detected in all four sheep breeds. The genotype distribution at the G1 and G4 loci had significant differences between the low-prolificacy sheep breed and the other three high-prolificacy sheep breeds. There was no difference in the genotype distribution at the G1 and G4 loci between the three high-prolificacy sheep breeds. Haplotype analysis of the four polymorphic loci in suggested that H4 (GGAA) was the preponderant haplotype in the three high-prolificacy sheep breeds, but H1 (GGGG) was in the low-prolificacy sheep breed. These results preliminarily showed that the and might be major genes influencing the prolificacy of Chinese sheep breeds.