The polymerase chain reaction (PCR) was used to amplify a 99 bp region from the kappa-casein gene of Holstein dairy cattle which contains the nucleotide substitutions diagnostic of the 2 major protein variants of kappa-casein. Identity of the amplified product was confirmed by direct sequencing. Digestion of the PCR product with MboII (A variant specific) or TaqI (B variant specific) allowed direct determination of the genotype of the animal (homozygous or heterozygous). A total of 58 lactating cows with known kappa-casein phenotype were tested using PCR. In all cases, the measured genotype confirmed the phenotype. We also determined the genotype of 42 proven bulls using this methodology and compared the assigned genotype with progeny data obtained by protein analysis. Since neither progeny testing- to indirectly assess the contribution of the sire nor sexual maturity of the animal is required to test the genotype at the DNA level, kappa-casein genotype can be identified at an earlier stage of development. This allows for the possibility of more rapidly changing gene frequencies in the population by selection, if desirable.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume XIV. Dairy cattle genetics and breeding, adaptation and conservation., , 251–254, 1990
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