| IGF-II which is also named Somatomedin A, is one of the insulin-like growth factor releasing growth factors family members.It was proved that IGF-II is the most important growth factor for mitosis of rodents. IGFs are middle messenger of growth hormone signal.When IGFs interact with growth hormone, IGFs function in target organs and promote growth and development. The cel1s culture experimentation indicated that IGF-II is myocyte growth autocrine signal. The concentration of IGF-II can affect the multiplication and differentiation of muscle fibre. During muscle fibre differentiation, the content change of IGF-I receptor also showed that IGF-II has important effect for muscle fibre differentiation. IGF-II regulates some kinds of metabolisms and is an important factor in animal embryo development.The level of IGF-II contents in circulation system will affect the dissociative fatty acid content and abdominal fat weight,which indicated that lipid metabolism was directly or indirectly affected by IGF-II.The pathway of phosphoric acid tyrosine kinase of IGF-I receptor is mainly signal pathway for inducing lipid cell differentiation.However,the study results showed that IGF-II don't combine with IGF-II receptor.IGF-II maybe conduct signal by IGF-I receptor and induce fat cell differentiation and affect 1ipid metabolism.The fatness traits are controlled by multiple genes.Understanding the genetic control of fat metabolism in swines will provide an opportunity for genetic enhancement of fatness traits. The study of candidate gene is one of the primary methods to determine whether specific genes are related to economic traits in farm animals.In addition, the population used for the candidate gene approach doesn't need specified designed.IGF-II gene is a growth factor mainly expressed in fetus, but it influences growth performance after birth in livestock, and this gene was subjected to imprinting in mammals.The candidate gene approach is a powerful method for finding the QTLs responsible for genetic variation in the traits of interest in agricultural animal species. The QTL affecting muscle growth, fat deposition and heart size was first identified in intercrosses between the European wild boar and Large White domestic pigs and between Pie′train and Large White pigs. The alleles from the Large White breed in the first cross and the Pie′train breed in the second cross increased muscle mass and reduced back-fat thickness. The QTL explained 15–30% of the phenotypic variation in muscle mass and 10–20% of the variation in back-fat thickness. Some Single Nucleotide Polymorphisms (SNPs)sites were found associated with fatness traits in IGF-II gene of hum and swine. In addition,experiment showed that the pig fat deposition was affected by IGF-II gene.Therefore, IGF-II gene can be taken as the candidate gene which impact swine fatness traits. The objectives of this study were to identify polymorphisms of IGF-II gene,deve1op PCR-SSCP methods to detect those DNA polymorphisms in different populations,and evaluate associations between IGF-II polymorphisms and growth and fatness traits.PCR-SSCP and PCR-RFLP technologies were applied to detect the polymor-phisms of IGF-II gene exon 1, exon 2, exon 3, exon 4, exon 4b, exon 5, exon 6, exon 7, exon 8, exon 9, intron 2, intron 8 in Songliao Black pigs. The associations between these polymorphisms and growth and Carcass traits were analyzed using the SPSS general linear model (GLM).According to detection outcome of PCR-RFLP, we learned that polymorphism of intron2 was detected in the NciI sites.The frequencies of A allele gene was 0.6087, The frequencies of B allele gene were 0.3913 respectively. Songliao black pig only showed AA and BB in the NciI site. The polymorphism of intron8 wasn't detected. The polymorphism fragments were cloned and sequenced. The sequencing results indicated that there were three single nucleotide mutation: G→A,T→C and T→C in the intron2 of the IGF-II gene.The polymorphism of the IGF-II gene in Songliao black pig was analyzed by PCR-SSCP. The results showed that the polymorphisms were not detected by PCR-SSCP in the exon3, exon5, exon6, exon7 and exon8 of the IGF-II gene. And two alleles, A, and B, three genotypes, AA, AB, and BB, were detected in the exon1, exon2, exon4, exon4b and exon9 of the IGF-II gene. The homozygous individua1s of diffetent genotype were cloned and sequenced.The sequencing results indicated that there was one single nucleotide mutation: T→C in the exon1, three single nucleotide mutation: G→A, T→C, G→A in the exon2, one single nucleotide mutation: G→C in the exon4, one single nucleotide mutation: G→A in the exon4b, three single nucleotide mutation: C→A, A→T, T→C in the exon9.The Chi-square test for goodness of fit showed that the frequencies of the IGF-II genotypes in the population of Songliao black pigs agreed with Hardy-Weinberg equilibrium.The genetic correlations were obtained between genotypes of the exon1, exon2, exon4, exon4b, exon9 and intron2 of IGF-II gene and growth and carcass traits by the least square analysis. The results indicated that the mutation in exon1 significantly affected lean percentage and flesh color, the mutation in exon2 significantly affected ripe meat rate, the mutation in exon4 significantly affected lean percentage,average backfat thickness,average daily gain, the mutation in exon4b significantly affected lean percentage,average daily gain, the mutation in exon9 significantly affected average backfat thickness,average daily gain, the mutation in exon1 significantly affected average daily gain after weaning. Average daily gain after weaning. Therefore, the genetic analysis of IGF-II gene revealed that IGF-II locus significantly affected average daily gain after weaning, lean percentage,and average backfat thickness.There were no significant associations between the SNP and other body composition traits such as LMA,SH,TN and WLR.The software SHEsis was also used to make haplotype analysis. There was a weak linkage disequilibrium between exon4 and exon4b,exon4 and exon9.The IGF-II gene is,therefore, a potential marker for use in molecular as sisted selected programs.It could be preliminarily deduced that IGF-II gene was probably a major gene or a QTL linked gene which associated with growth and carcass traits in pig.
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