| Using PCR-SSCP and DNA sequencing techniques, genetic variations of 14 loci of insulin-like growth factor-I (IGF-I) and its receptor (IGF-IR) genes were detected in 708 individuals of two Chinese dairy goat breeds (Guanzhong and Xinong Saanen). Their genetic structure and diversity were analyzed, too. Association analysis were carried out by using SPSS software(16.0) and Least Square Analysis method on milk production traits and body size traits at the candidate genes of the above-mentioned breeds. The objects were to discover the hereditary characteristics of these dairy goat breeds, to explore genetic markers with significant effects on economic important traits for efficient selection, and to provide genetic information for the dairy goat breeding program. The results were as follows:1. Polymorphisms of IGF-I gene in two dairy goat breedsThe variations of five loci (P1P5) in IGF-I gene were detected in Guanzhong and Xinong Saanen breeds. These loci contained exon1W, exon1, exon3, exon4, exon5 and their partial introns. In those five loci, only P1 and P4 loci demonstrated polymorphisms, locating in 5'- flanking region and intron 4, respectively. Compared with goat IGF-I gene sequence published in GenBank (D26119.2), the polymorphisms were caused by two novel mutations namely g.1617 G > A and g.5752 G > C.Chi-square test results were as follows: in P1 locus, both Guanzhong and Xinong Saanen dairy goats were in Hardy-Weinberg equilibrium (P>0.05). Genetic diversity indexes (Ne/PIC/He) were 1.16/0.13/0.14 and 1.23/0.17/0.19 respectively. In P4 locus, Xinong Saanen dairy goat was in Hardy-Weinberg equilibrium (P>0.05), but Guanzhong breed was not (P<0.01). Genetic diversity indexes (Ne/PIC/He) were 1.43/0.26/0.3,1.72/0.33/0.42 for Guanzhon and Xinong Saanen. The result illustrated that, P4 locus owned abundant polymorphic information (0.25R9) in IGF-IR gene, which included exon 1 to exon 10 (without exon 7) and their partial introns were analyzed in 2 dairy goat breeds. Only two (R8 and R 9 loci) of them demonstrated the polymorphisms. Both the loci had three kinds of genotypes(CC, CT and TT). In locus P8, the C>T mutation in exon 9 was found for the first time (NC007319: g26688 C>T). The mutation resulted in Leu 608 Leu in IGF-IR protein. The polymorphism in P9 locus was caused by T>C mutation in intron 10 (NC007319: g28273 T>C).Chi-square test results were as follows: R8 and R9 loci were not in Hardy-Weinberg equilibrium in the two breeds (P<0.01). Genetic diversity indexes of Ne/PIC/He in Guanzhong and Xinong Saanen dairy goats were 2.00/0.37/0.50, 1.97/0.37/0.50, respectively at P8 locus and 1.99/0.37/0.50, 1.95/0.37/0.50 respectively at R9 locus. The results illustrated that both the R8 and R9 loci owned abundant polymorphic information (0.250.05). In the milk composition, Xinong Saanen dairy goats with CC genotype had heavier milk density than the CT ones (P<0.05), and the milk density difference between the individuals with TT genotype and CT one was not significant.Three kinds of genotypes (CC, CT and TT) were detected at R9 locus, too. TT genotype was the majority one. Different genotypes at this locus did not have any significant influence on milk production traits in Xinong Saanen dairy goats. In Guanzhong breed, the body heights of individuals with CC genotype were greatly significantly higher than those with CT genotype (P<0.01), and the goats with TT genotype had higher body heights than CT one (P<0.05). The individuals with CC genotype were longer in body length than those with TT (P<0.05). In Xinong Saanen dairy goats, individuals with TT and CT genotypes had higher body heights than those with CC genotypes (P<0.05). Different genotypes did not influence significantly on the body length and chest circumference.The result illustrate that, the polymorphism at P8 locus had association with the milk density in Xinong Saanen breed; different genotypes at P9 locus had great significant or significant influence on the body size in both breeds.
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