Analysis Of The SNPs Of The Leptin Gene And Their Associations With Growth Traits In Four Sheep Breeds

Using the methods of"random sampling in typical colonies", 121 Poll Dorsets, 72 Suffolks, 73 Texels and 89 Tan sheep were sampled. PCR-SSCP was applied to detect single nucleotide polymorphism (SNP) of exon 2 and exon 3 of the Leptin gene for these 358 sheep, also we analyzed on associations of SNPs of Leptin Gene with growth traits in the four sheep breeds. The molecular phylogenetic tree was constructed by MEGA 4 among different species, including sheep, goat, water buffalo, cattle, pig, human, house mouse and chicken. The results are as the following:(1) There is no SNP in exon2 of the Leptin gene, four SNPs were detected in parts of intron 2. They are A99G, G115A, C150T and C171T. The G115A and C171T are new SNPs. Three SNPs occurred in exon 3. They are G271A, C316A and G387T SNPs. Also we detected four combined genotypes, they are A99G and C150T, A99G and G115A, A99G and C316A, A99G and G387T. The C171T SNP is only in the breed of Poll Dorsets. The C316A, A99G+G115A and A99G+C316A SNPs only exist in the breed of Texel. The G387T and A99G+G387T SNPs are only detected in Tan sheep, which are the characters of the breed of Tan sheep. (2) The frequencies of seven SNPs and combined genotypes in the four sheep breeds are all low. The SNPs detected in Tan sheep are much more than other breeds. The genotype frequencies of A99G SNP in TX and G271A SNP in Tan are not agreed with Hardy-Weinberg equilibrium(P<0.01), which of other SNPs in four breeds accord with Hardy-Weinberg equilibrium(P>0.05). The allele frequency distributions among different sheep breeds at the A99G, C150T and A99G+C150T polymorphic sites are significantly different.(3) The 441bp of exon 2 and exon 3 of Leptin gene in sheep was amplified and compared the nucleotide sequence of coding region with the homologous Leptin genes in other seven species retrieved from the GenBank, they are goat, water buffalo, cattle, pig, human, house mouse and chicken. And finally a phylogenetic tree was constructed by Minimum Evolution (ME), Maximum Parsimony (MP), Neighbor-Joining (NJ) methods using the coding region DNA sequence of the Leptin gene in all species. The results of the three methods of the molecular phylogenetic tree and the homologies of the coding region of Leptin gene are the same: The relationship between sheep and goat is the closest, and the genetic distance between them is the shortest. The relationships between sheep and water buffalo, cattle, pig, human, house mouse, chicken are gradually further, and the genetic distances are gradually longer.(4) The associations between some factors and growth traits were analyzed. The association between breeds and growth traits are significant(P<0.01). There is no association between sex and growth traits(P>0.05). Also there is no association between all SNPs and growth traits(P>0.05).