| The prolificacy of sheep was affected by many factors, such as genetic, age, season, nutrition, and so on. Genetic was the most important one. In some instances, the differences in ovulation rate have been attributed to the action of a single or a closely-linked group of genes. Mutations in these genes may change litter size of sheep. In the present research, the polymorphism of A746G of bone morphogenetic protein receptor IB (BMPR-IB), FecXG and FecXL locus of bone morphogenetic protein 15 (BMP15), exon 1 and exon 2 of growth differentiation factor 9 (GDF9), intron 9 and exon 10 of prolactin receptor (PRLR), exon 1 of estrogen receptor (ESR) and the 5` flanking region of insulin-like growth factor-I (IGF-I) gene in 330 sheep of eight breeds or strains, which including Small Tail Han (STH), Poll Dorset (PD), Suffolk (S) Germany Mutton Merino (GMM) and Chinese Merino (Xinjiang type) (including Prolific strain (PS), Meat strain (MS) and Large Frame strain (LFS) ), were detected and the relationship between genotypes and average litter size were analyzed. The results showed that (1) the A746G mutation in BMPR-IB gene was found not only in STH but also in PS, MS and S. Whereas B allele of the A746G mutation was the dominant gene only in STH population. The average litter size of BB genotype was 1.89 and 0.97 greater than those with genotype + + and B+, and B+ was more than 0.92 compare to that of ++ in Han sheep (P<0.01). But the different was not observed in PS. The results indicated that there was a significant positive correlation between B allele and prolificacy in STH, which could be used for the selection the prolificacy individual of STH. However, there was no correlation between B allele and litter size in other breeds or strains. (2) The polymorphism of FecXG locus of BMP15 was not detected in these 8 pupolations. A novel mutation, G1047A, was found in FecXL locus. However the new-found mutation did not affect the coding amino acid of sheep BMP15. There was no correlation between genotypes and average litter size of this locus. (3) The polymorphism in exon 1 of GDF9 was not found by PCR-SSCP in the 8 breeds/strains, but the known G4 mutation in the exon 2 of GDF9 gene was detected in these breeds/strains. However, further analysis displayed that the correlation between genotypes and litter size did not exist. (4) A C→T at No.259bp in PRLR intron 9 was found. The average litter size of BB genotype of this mutation was 0.81 and 0.87 more than that with AA and AB genotype in STH (P<0.05). In addition, four mutations, including G→A, G→A, C→G, and C→T, at No.304, 571, 585 and 606bp in PRLR exon 10 were found, respectively. Among these mutations, 304G→A, 571G→A and 585C→G leaded Glu changed to Lys at 378, Ala to Thr at 476, Ser to Arg at 480 in sheep PRLR, respectively. For the 304G→A, the average litter size of AB genotype was 0.58 and 0.80 greater than those with AA and BB genotype in PS population (P<0.05). In STH, the average litter size of the AB was 0.80 greater than that of AA genotype of 571G→A mutation. (5) Single nucleotide polymorphisms of exon 1 of ESR gene were detected by PCR-SSCP. No polymorphism was detected in the amplified region in the eight sheep breeds/strains. (6) PCR-SSCP analysis and DNA sequencing of the 5'flanking region of IGF-I revealed that there were two mutations, G→C and G→A, located at -651bp and -649bp upstream of initiator ATG. In STH, the average litter size of the AA and AB was 1.2 and 1.45 greater than that of BB genotype (P<0.05). In PS strain, the mutation has the tendency to increase the litter size. The average litter size of AB genotype was 0.67 greater than that of AA genotype in PS (P=0.077). In other population, the difference was not detected.These results suggested that species differences must be considered for prolificacy individual selection. For genetic selection, respective prolificacy genotype should be based on, such as BB genotype of A746G mutation in BMPR-IB gene for STH, AB genotype of G304A mutation in PRLR exon 10 for PS. For other sheep breeds or strains, the major genes controlling prolificacy require further study.
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