Nucleotide sequencing and DNA polymorphism studies of beta- lactoglobulin gene in native Saudi goat breeds in?relation to milk yield

摘要

β-Lactoglobulin (β-LG) is the dominant non-casein whey protein found in milk of bovine and of most ruminants. The amino acid sequence of β-LG along with its 3-dimensional structure illustrates linkage with the lipocalin superfamily. Preliminary studies in goats indicated that milk yield can be influenced by polymorphism in genes coding for whey proteins. The aim of this study is to identify and evaluate the incidence of functional polymorphisms in the exonic and intronic portions of β- LG gene in native Saudi goat breeds (Ardi, Habsi and Harri). Blood samples were collected from 300 animals (100 for each breed) and genomic DNA was extracted using QIAamp DNA extraction kit. A fragment of the β- LG gene from exon 7 to 3' flanking region was amplified with pairs of specific primers. Subsequent digestion with Sac II restriction endonuclease revealed two alleles ( A and B ) and three different banding patterns or genotypes, i.e. AA , AB , and BB . The statistical analysis showed that β- LG AA genotype had higher milk yield than β- LG AB and β- LG BB genotypes. Nucleotide sequencing of the selected β- LG fragments was done and submitted to GenBank NCBI (Accession Nos. KJ544248, KJ588275, KJ588276, KJ783455, KJ783456, KJ874959, and KP269078). Two already established SNPs in exon 7 (+4601 and +4603) and one fresh SNP in the 3’ UTR region were detected in the β- LG fragments with designated AA genotype. The exonic SNPs, i.e. +4601 (G/A) and +4603 (G/C), were found within the Sac?II restriction site and accountable for generating the AA genotypic patterns. Hence, the allele characterized by the substitution G>A has been sub-designated as AAA , while the one characterized by the substitution G>C as AAC. The polymorphisms in exon 7 did not produce any amino acid substitution.