Genetic variations of β- and K-casein genes in Egyptian sheep breeds
AbstractObjective: Casein genetic polymorphisms are important and well known due to their effects on quantitative traits and technological properties of milk manufacturing. The casein fraction of ruminant milk proteins consists of four caseins, namely 8s1-, 8s2-, β-and K-casein. At the DNA level, polymerase chain reaction (PCR) and single-strand conformation polymorphism (SSCP) allow for the simultaneous typing of several alleles at casein loci, as well as the detection of unknown polymorphisms. The genetic polymorphism of two ovine milk protein casein genes, β- and K-caseins, was studied in sheep animals belonging to three main breeds reared in Egypt (Rahmani, Barki and Ossimi), as a tool for genetic improvement of milk trait characteristics. Methodology and results: SSCP of β-casein exon 7 revealed two different patterns in eighty-five tested animals. The sequence analysis of the PCR product (299-bp) of these two different patterns showed two single nucleotide substitutions; A®C and C®T without any amino acid exchange. The frequencies of these two different patterns were 96.67% and 3.33% in Rahmani; 65.52% and 34.48% in Ossimi and 88.46% and 11.54% in Barki, respectively. The nucleotide sequence of 9-casein in Egyptian sheep was submitted in database NCBI/ GenBank with the accession number JX080379. The polymorphism of Kcasein gene was also detected in eighty-six animals using PCR-SSCP technique. PCR amplified a fragment with 406-bp in exon 4 of this gene. SSCP results showed that all tested sheep animals are monomorphic. The alignment between our sequences with published sequence revealed two nucleotide substitutions; C®T and T®C. The nucleotide sequence of K-casein in our tested animals was submitted in database NCBI/ GenBank with the accession number JX050176. Conclusion and application of findings: This study aimed to identify the genetic polymorphism of β and Kcasein genes, which are strongly related to economically important milk quantitative traits in some Egyptian sheep breeds, as a tool or genetic markers for improvement of these breeds. Key words: Sheep, β-casein, K-casein, PCR-SSCP, SNP.
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