Studies On SNPs Of DGAT1 Gene And Its Association With Milk Production Traits In Dairy Cattles

The purpose of this study was to detect single nucleotide polymorphisms (SNPs) within DGAT1gene, to investigate its effects on milk production traits of the three dairy breeds. Based on the Holstein DNA sequences of DGAT1 gene exon 8 and 3'-UTR in GenBank, two primer pairs were designed for PCR. SNPs of DGAT1gene from three different dairy breeds were detected by single strand configuration polymorphisms (SSCP). The genetic structure of the three populations at polymorphic loci, and the associations of milk production traits does with DGAT1gene were also explored. The results are as follows:1,In the three breeds,DGAT1 gene were found in exon8 of the three genotypes KK, KA, AA and 3'-UTR of the three genotypes MM, MN, NN;the former genotype frequencies are as follows: New Zealand Holstein of 0.37,0.43,0.20, Australia Holstein of 0.34,0.43,0.23, Chinese Holstein of 0.08,0.48,0.44.The latter genotype frequencies are as follows: New Zealand Holstein of 0.1048,0.2476,0.6476, Australia Holstein of 0.0709,0.2482,0.6809, Chinese Holstein of 0.0467,0.2933,0.6600; Theχ2 test showed that the three breeds in the 3'-UTR region locus were not in Hardy-Weinberg equilibration significantly(P<0.01) and in Hardy-Weinberg equilibration significantly in exon8(P>0.05).2,Homozygous sequencing showed that: A GC→AA mutation at 10433-10434 bp of exon8 of DGAT1 gene in genotype KK. This mutation resulted in an amino acid change: lysine→lactamine.A GT→CA mutation at 11992-11993bp of 3'-UTR of DGAT1 gene in genotype MM.A GT→CA mutation at 11992-11993bp and a T→G mutation at 11989 of 3'-UTR of DGAT1 gene in genotypeNN.3,The results of population genetic characteristics analysis show that: Gene heterozygosity of 3'UTR are: New Zealand Holstein of 0.4898,Australia Holstein of 0.4843,Chinese Holstein of 1.8854;effective number of alleles are as follows: New Zealand Holstein of 1.9600,Australia Holstein of 1.9391,Chinese Holstein of 1.8854; PIC values are as follows:New Zealand Holstein of 0.3699,Australia Holstein of 0.3670,Chinese Holstein of 0.3593. Gene heterozygosity of exon8 are: New Zealand Holstein of 0.4853,Australia Holstein of 0.4943,Chinese Holstein of 0.4352;effective number of alleles are as follows: New Zealand Holstein of 1.9429,Australia Holstein of 1.9775,Chinese Holstein of 1.7705; PIC values are as follows:New Zealand Holstein of 0.3675,Australia Holstein of 0.3722,Chinese Holstein of 0.3405.The value of gene heterozygosity of the two locus are not high and the degree of variation is only in the middle level; Effective number of alleles are relatively close to the number of test alleles 2 and allele in the populations is more evenly distributed; The PIC values of the three breeds are in between 0.25-0.5 to moderate polymorphism.4,The results of correlation analysis show that:There were significant associations between 3'-UTR genotypes and milk protein percentage and milk yield in Australia Holstein (P <0.05).MM-type individuals have higher milk yield and lower milk protein. MM-type individuals have higher milk yield in New Zealand Holstein breeds(P <0.05).There were significant associations between exon8 polymorphism and milk fat percentage in Chinese Holstein breeds;MM-type individuals have 0.16 or 0.27 percentage point more than those with genopype KA and AA ,respectively;In Australia Holstein breeds, the does with genotype KK, respectively,but had milk protein percent lower than those with genotype KA or AA, respectively; In New Zealand Holstein breeds, the does with genotype KK milk fat percent more than those with genotype KA or AA, respectively.Previous studies showed that, DGAT1 gene was major gene with milk traits ,or was associated with the QTL influencing milk traits.This study proves the view. It should be feasible to implement the marker assisted selection of milk traits by using the two polymorphic site s of amplification production of the primer PU3 and PE8.