Study On Candidate Genes Related To High Prolificacy In Small Tail Han Sheep

To detect the polymorphisms of IGF-Ⅰ,IGF-Ⅱand NPY gene in precocious puberty and high prolificacy breed (Small Tail Han sheep and Hu sheep) and late maturity and low prolificacy breeds (Texel and Dorset), PCR-SSCP, PCR-RFLP, sequence analysis and gene cloning were used. The relation between the polymorphisms and high prolificacy in sheep was also studied to provide a scientific basis for marker-assisted selection for prolificacy in sheep The results were as follows.1. The products amplified by primers P1 and P2 displayed polymorphisms in IGF-Ⅰgene. For primer P1, six genotypes and three alleles were detected in Small Tail Han sheep (n=277), seven genotypes and four alleles in Hu sheep (n=58), two genotypes and two alleles in Texel (n=48), four genotypes and four alleles in Dorset (n=46). The ewes with genotype 123/123 bp had 0.81 (P<0.05) or 1.03 (P<0.01) lambs more than those with genotype 125/125 bp or 125/127 bp, the ewes with genotype 123/125 bp had 0.46 (P<0.05) or 0.68 (P<0.01) lambs more than those with genotype 125/125 bp or 125/127 bp, and the differences of the litter size between 123/123 bp and 123/125 bp, and between 125/125 bp and 125/127 bp were non-significant (P>0.05) in Small Tail Han sheep. For primer P2, three genotypes (AA, AB and BB) were detected in Small Tail Han and Hu sheep, two genotypes (AA and AB) in Texel, only one genotype AA in Dorset. Compared with AA genotype, there were two single nucleotide mutations (C→G) at 1511 bp and (A→G) at 1513 bp position of regulatory region of IGF-Ⅰgene in the BB genotype. The ewes with genotype BB or AB had 0.96 (P<0.05) or 0.38 (P<0.05) lambs more than those with genotype AA, and the difference of the litter size between BB and AB genotypes was non-significant (P>0.05) in Small Tail Han sheep.2. Only the product amplified by primer P1 displayed polymorphism in IGF--Ⅱgene. Three genotypes (GG, GA and AA) were detected in four sheep breeds tested. Compared with GG genotype, there was a single nucleotide mutation (G→A) at 165 bp position of 5'regulatory region of IGF-Ⅱgene in AA genotype. No significant difference (P>0.05) was found in litter size between GG, GA and AA genotypes in Small Tail Han sheep. The results preliminarily indicated that the detected loci of IGF-Ⅱgene had no significant influence on the litter size in sheep.3. Only the product amplified by primer P1 displayed polymorphism in NPY gene. Five genotypes were detected in Small Tail Han sheep, three genotypes in Hu and Dorset, but only one genotype in Texel. Sequencing revealed that there were three alleles (CR, TR and TW) in Small Tail Han sheep, two alleles (CR and TR) in Hu and Dorset, only one allele (CR) in Texel. Compared with CR allele, there was one single nucleotide mutation (C→T) at 93 bp position of coding region of NPY gene in the TR allele. Compared with CR allele, besides C93T mutation, there was one double nucleotide mutation (GA→AT) at 130 bp and 131 bp position of coding region of NPY gene in the TW allele. This mutation caused an Asp→Ile replacement at position 16 of amino acid sequence of sheep NPY mature peptide. For C/T polymorphic site, the differences of the litter size between three genotypes were non-significant in Small Tail Han sheep (P>0.05). For GA/AT polymorphic site, the ewes with genotype RW had 0.56 (P<0.05) lambs more than those with genotype RR in Small Tail Han sheep. In the five combined genotypes of Small Tail Han sheep, the difference of the litter size between TTRW and CTRW genotypes was non-significant (P>0.05), the differences of the litter size between TTRR, CTRR and CCRR genotypes were non-significant (P>0.05), least squares means of litter size for TTRW and CTRW genotypes were significantly higher than those for the other genotypes (P<0.05).