| Because of its very low heritability of litter size of pig, the improvement of the litter size is limited by the conventional breeding technology. It is very important to find the major genes and the genetic markers related to the litter size. All reproductive pathways of animal will be mediated by procreant hormones, including generation and maturation of procreant cells, ejaculation, ovulation, pregnancy, secretion of milk and so on. Hence genes, which coding procreant hormones or their receptors, are presumed to be ideal candidate genes for reproductive traits.In the experiment, 481 pigs including Laiwu Black, Lulai Black, Licha Black, Luyan White, New Yimeng Black, Yorkshire, Landrace and Duroc were selected to study genetic variants. The purposes of this study were to detect single nucleotide polymorphisms (SNPs) within BMP15 gene and BMPR-IB gene, to analyze the genetic structure of eight pig breeds, and to investigate the effects of the two genes on litter size of eight pig breeds. Based on the bovine and ovine DNA sequences in GenBank, primer pairs for BMP15 gene (AF458070) and BMPR-IB gene (AY157623) were designed for PCR respectively. Based on the bovine and ovine DNA sequences in GenBank, Amplified regions included exons of BMP15 gene and BMPR-IB gene. In five Shandong local breeds and three foreign pig breeds by PCR-SSCP The genetic structure of the three populations at polymorphic loci, and the associations of the litter size of eight pig breeds does with the two genes were also explored. The results are as follows:For BMP15 gene, In Shandong local breeds, Laiwu Black and Lulai Black, the preponderant alleles is A allele, the genotype frequency was AC>AA>CC. In New Yimeng Black and Licha Black, the preponderant alleles was C allele, the frequencies of allele A and C in Shandong local pig is higher than 0.5; In foreign pig breeds, Yorkshire and Landrace, the preponderant alleles is B allele, among this three pig breeds, the frequency of the allele A was highest in Duroc (1.0000)the frequency of BB genotype was significantly higher than the others. The results of Chi square showed that, except the Luyan White, Yorkshire and Duroc, all the other population fitted the H-W equilibrium situation(P>0.05). For BMP15 gene, in AA genotypic sows, the average TNB and NBA of foreign pig breeds was 1.20 and 1.64 more than that of Shandong local breeds, respectively (P<0.05); in CC genotypic sows, the average TNB and NBA of foreign pig breeds was 1.20 and 0.82 more than that of Shandong local breeds, respectively (P<0.05).For BMPR-IB gene, In Shandong local breeds, Laiwu Black, Lulai Black Licha Black and Luyan White, the preponderant alleles is B allele, the frequencies of allele B is higher than 0.5. New Yimeng Black, the preponderant alleles is B allele, the frequencies of allele B is 0.7308. the frequency of genotype AA in Laiwu Black and New Yimeng Black is highest, the frequency of genotype BB in Lulai Black is highest; In foreign pig breeds, Yorkshire, Landrace and Duroc, the preponderant alleles is A allele, the frequencies of allele A is higher than 0.5, the frequency of genotype AB in Landrace Black and Yorkshire Black is highest. The results of Chi square showed that, Licha Black, Luyan White and Landrace fitted the H-W equilibrium situation(P>0.05). in Shandong local breeds, the average TNB and NBA of AA was 0.49 and 0.51 more than that of BB, respectively (P>0.05); while the average TNB and NBA of BB was 1.05 and 0.90 more than that of AA in the foreign pig breeds, respectively (P<0.05).Age is one important factor influencing of prolificacy, the TNB of first born is less than the TNB of the still-born, so does in the NBA. In this research the effects of BMP15and BMPR-IB on prolificacy is proved to be obvious, and they are abundant in polymorphism. From these results we can putatively drew the conclusion that these two genes could be used to select the pig for high reproduction trait in molecular marker assisted selection programs, in order to improve the level of prolificacy.
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