Bovine <i>β</i>-casein: Detection of two single nucleotide polymorphisms by bidirectional allele specific polymerase chain reaction (BAS-PCR) and monitoring of their variation

Abstract

Due to the functional importance of bovine milk protein polymorphisms, their correct discrimination is of great interest both from a scientific and practical point of view. Nowadays a large number of commercial platforms are available for semi-automated or fully automated SNP genotyping. However, in some cases the use of simple and rather cheap methods is an effective tool to be implemented within one's own laboratory for the routine analysis of a specific SNP. The present paper describes two simple tests based on the bidirectional allele-specific polymerase chain reaction (BAS-PCR) developed for the identification of β-casein (CSN2) B and I genetic variants. The practical application of the two methods on a panel of 84 Italian Brown bulls and 100 Italian Friesian cows is also discussed, including the biological significance of the two genetic variants and the importance of taking their occurrence into account when linkage analyses are performed on milk functional properties. A combined system for analysing milk protein variants by isoelectrofocusing (IEF) and the BAS-PCR assay developed for CSN2*I is described.

Genetic variation and effects of candidate-gene polymorphisms on coagulation properties, curd firmness modeling and acidity in milk from Brown Swiss cows

“…Here, the B allele (frequency, 0.16) was overrepresented compared with the A 1 allele (0.07) in the CSN2 rs43703011 allele C genes. This finding is similar to that from a previous report on the Brown Swiss (Chessa et al, 2013). At present, it is not possible to establish whether the less favorable effect of the CSN2 rs43703011 A variant on RCT is due to the presence of the A 1 or B alleles, and the positive effect of the CSN2 B allele reported by Bittante et al (2012) remains controversial.…”

“…Thus, even if the other CSN3 loci failed during the analysis (possibly because these SNPs are too close together, compromising primer hybridization), the frequency of the B allele in our population could be estimated at about 0.78. This was even higher than that found by Chessa et al (2013), who reported it increasing from 0.64 to 0.71. This indicates that selection is rapidly increasing the frequency of the B allele.…”

“…At present, it is not possible to establish whether the less favorable effect of the CSN2 rs43703011 A variant on RCT is due to the presence of the A 1 or B alleles, and the positive effect of the CSN2 B allele reported by Bittante et al (2012) remains controversial. Moreover, the CSN2*A 2 variant is usually found in a haplotype with the CSN3*B variant (frequency, 0.56 to 0.67; Chessa et al, 2013), suggesting that the positive effect of the CSN2 rs43703011 C allele could be confused with that of the CSN3*B variant. Notably, the casein genes were previously reported to show varied associations with MCPs (Caroli et al, 2009).…”

Detecting β-Casein Variation in Bovine Milk

“…In 2005, Dutch Holstein Friesian A 2 plus I accounted for 0.692, A 1 for 0.285, A 3 for 0.001, and B for 0.022, showing an increase in the frequency of β-CN A 2 at the expense of β-CN A 1 compared to a previous study carried out in 1989 [19]. Conversely, in Italian Friesian no substantial modification of the frequency of β-CN variants was found in a 10-year period [20]. In Swedish Holstein, the frequencies of β-CN A 2 , β-CN A 1 , and B were 0.60, 0.34, and 0.06, respectively [18].…”

“…As an example, we refer to Holstein Friesian which is the most common dairy breed, spread all over the world for its high milk yield. In Italian Friesian, the frequency of β-CN A 2 plus I variants accounted for 0.570, followed by A 1 (0.395), and B (0.035) [20]. It is necessary to point out that A 2 and I variants comigrate in IEF, but these variants differ for one amino acid exchange (Met 93 in A 2 to Leu 93 in I) not affecting Pro 67 , which is carried by both polypeptides [21].…”