Studies On Polymorphism Of BMPR-IB Gene And Its Correlation With Litter Size In Sheep Populations

Genetic variation of bone morphogenetic protein receptor type IB (BMPR-IB) gene sequence was analyzed by PCR-RFLP in Small Tailed Han Sheep, Poll Dorset sheep, and their F1 hybrid sheep and F2 hybrid sheep. From the analysis, genetic characteristics of BMPR-IB gene in sheep were identified and effective molecular markers for assisted selection of sheep prolificacy were obtained. Two mutation sites of BMPR-IB gene were found in the present study. One was 746 A→G, this mutation resulted in amino acid change of glutamine→arginine. The other one was 1113 C→A, this mutation didn't cause a corresponding change in amino acid sequence.BMPR-IB gene of 201 of Small Tailed Han ewes,27 F1 hybrid ewes,26 Poll Dorset sheep,123 F1 hybrid rams and 21 F2 hybrid sheep were detected by PCR-RFLP. The results indicated that the allele frequency of B and+in Small Tailed Han Sheep were 0.454 and 0.546, genotype frequency of BB, B+and++were 0.176, 0.556 and 0.268; Poll Dorset had only+allele; in F1 hybrid sheep, allele frequency of B and+were 0.097 and 0.903, genotype frequency of BB, B+and++were 0.193 and 0.807; in F2 hybrid sheep, allele frequency of B and+were 0.143 and 0.857, genotype frequency of BB, B+and++were 0.286 and 0.714. The independence test showed that gene distribution in F1 hybrid and Small Tailed Han Sheep had significant difference (P<0.01), and gene distribution in F2 hybrid and Small Tailed Han Sheep, Poll Dorset were significantly different (P<0.05). Theχ2 test showed that,χ2 values of BMPR-IB gene amplified fragments in Small Tailed Han Sheep, Poll Dorset, F1 hybrid and F2 hybrid (P>0.05) did not reach significant level and accorded with the Hardy-Weinberg equilibrium. By analysis of polymorphism information content, Small Tailed Han Sheep had intermediate polymorphism, F1 and F2 hybrid had low polymorphism, and Poll Dorset did not have polymorphism.The average litter size of BB type was 0.73 (P<0.01) and 1.40 (P<0.01) more than that of B+type and++type in Small Tailed Han Sheep and F1 hybrid sheep with littering records and showed a good genetic advantage. Litter size of B+type was 0.45 (P<0.05) more than++type in F1 hybrid sheep (without BB type). Theχ2 test showed that BMPR-IB gene were not in Hardy-Wenberg equilibrium in the populations of Small Tailed Han Sheep and F1 hybrid. The results provided further verification that the BMPR-IB gene was one of the major gene for prolificacy of Small Tailed Han Sheep.