Single nucleotide polymorphisms of the exon7, 8, 9 of the porcine IGF2 gene were tested using PCR-SSCP. Genetic effects of the IGF2 gene on birth weight, weaning weight, six-month weight and six-month backfat thickness were analyzed. On the basis of the published DNA sequence (AY044828) of the porcine IGF2 gene, three pairs of primers were designed, and one polymorphism, three genotypes were found in the PCR product amplified with Ex8 primers. C-->T transition at 53 site of exon8 was detected by sequencing the homozygotes. The results showed that: firstly, the genotype distribution was not consistent among the different pig breeds. No significant differences (P > 0.05) were found in the genotype distribution when compared the Landrace with the Large White , the Laiwu with the Dapuliang, and the Yimeng with the Licha Black pig breeds, whereas significant differences (P lt; 0.01) were found among other tested pig breeds in the genotype distribution. Secondly, on the basis of the fixed effect model, significant differences (P lt; 0.05) were found in birth weight and six-month backfat thickness, whereas no significant differences (P > 0.05) existed in weaning weight and six-month weight. Thirdly, using least square analysis, it was shown that individuals of the BB genotype have significantly lower (P lt; 0.05) birth weight than those of AA and AB genotypes, with the order being AB > AA > BB ; Individuals of the AA genotype have significantly lower (P lt; 0.05) six-month backfat thickness than those of AB and BB genotypes, with the order being BB > AB > AA. These results suggest that IGF2 gene has significant effects on individual birth weight and backfat thickness. The IGF2 gene can be used in marker-assisted selection to accelerate the breeding progress.
[Show abstract][Hide abstract] ABSTRACT: The IGF-1 gene has been implicated as a candidate gene for the regulation of pig growth traits. We analyzed exons 3 and 4 of IGF-1 gene polymorphisms of the Banna mini-pig (28), the Tibetan mini-pig (30), the Junmu pig (55), and L. Yorkshire species (50) using PCR-SSCP. Three genotypes in exon 3 and 6 genotypes in exon 4 were observed, among which, one single nucleotide polymorphism, G201A, on exon 3 and two single nucleotide polymorphisms, A440G and T455C, on exon 4 were found. Statistical analysis of genotype frequencies revealed that the A allele was dominant in the large pig at the G201A locus (PIC = 0.20-0.34), and the AT alleles were dominant in the large pig at the A440G and T455C loci (PIC = 0.30-0.60). The genotype distribution between the various groups was significantly different (P< 0.01), with the highest heterozygosity seen in Junmu pigs at 0.223 and the lowest seen in L. Yorkshire at 0.098. The genetic distance of the Junmu pig from the L. Yorkshire is the smallest, the distance from the Tibetan miniature pigs is larger, and the distance from the Banna mini-pig is the largest. The IGF-1 gene polymorphism and heterozygosity results from various pig breeds indicate that IGF-1 is substantially polymorphic with significant difference of the polymorphic distribution and expression levels among various pig breeds. This information provides a theoretical basis for the genetic background of miniature pigs but also provides means to breed improved pig varieties.
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