STUDIES ON BIOCHEMICAL POLYMORPHISM OF MILK PROTEIN AS GENETIC MARKERS IN PIGS

Biochemical polymorphisms of sow's milk proteins, $\beta$-casein ($\beta$-CN), $\beta$-lactoglobulin ($\beta$-LG), post-lactoglobulin (post-LG), $\alpha$-lactalbumin ($\alpha$-LA) and X-protein, as genetic markers for major pig breeds (Landrace, Yorkshire, Duroc, Hampshire and cross bred) in Korea were determined by starch gel electrophoresis. Phenotype and gene frequencies at all marker loci were estimated and genetic differences among breed populations were analyzed. Three $\beta$-CN phenotypes (AA, AB and BB) controlled by two codominant alleles (${\beta}-CN^A$ and ${\beta}-CN^B$), four $\beta$-LG phenotypes (AA, AC, $AC^{\pm}$ and CC) controlled by two codominant alleles (${\beta}-LG^A$ and ${\beta}-LG^C$) and ten X-protein phenotypes (AA, BB, CC, DD, AB, AC, AD, BC, BD and CD) controlled by four codominant alleles ($X^A,\;X^B,\;X^C\;and\;X^D$) were identified. In addition, a genetically controlled polymorphism of post-LG was found for the first time in sow's milk protein. Three different phenotypes (AA, AB and BB) were designated $post-LG^A$ and $post-LG^B$. Of the five marker loci examined, $\alpha$-LA locus was observed to lack any individual variation in all breeds studied. All populations were in Hardy-Weinberg equilibrium for all loci. There were marked breed differences for phenotype and gene frequencies in the post-LG and X-protein marker loci. However, there were little differences between breeds in the gene frequencies at the $\beta$-CN and $\beta$-LG marker loci.