Restriction fragment length polymorphism analysis of the κ-casein locus in cattle

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Abstract
Summary The two common genetic variants (A and B) of bovine κ-casein originate from two point mutations in the codons for the aminoacids in position 136 and 148. These mutations give rise to polymorphic sites for the restriction endonucleases Hin dII, AluI, HinfI, MboII and TaqI. We have examined DNAs of several Italian Friesian cows and bulls of known and unknown genotype by Southern analyses using κ-casein cDNA probes. Restriction fragment length polymorphisms (RFLPs) specific for the A and B alleles were identified for each of the above enzymes, except for AluI, which has a non-polymorphic site 12bp away from the polymorphic one. We have also found two new polymorphic sites for MboII and TaqI in the non-coding regions. These sites differentiate the A allele into two new variants, named A1 and A2. The RFLP analysis permits the characterization of κ-casein alleles even in the absence of their expression. This should facilitate selective breeding programmes aimed at increasing the frequency of the κ-casein B allele whose product improves the cheesemaking properties of milk.