육우의 유전적 표식로서 유단백질의 다형현상에 관한 연구 = Studies on Polymorphisms of Milk Proteins as Genetic Markers in Beef Cattle

다국어 초록 (Multilingual Abstract)

Milk protein polymorphisms of as,-casein (αS₁-CN), β-casein (β-CN), κ-casein (κ-CN) and β-lactoglobulin (β-LG) loci as genetic markers for three imported beef cattle breeds (86 Angus, 92 Hereford and 32 Charolais) in Korea were analyzed by electrophoresis. On the basis of the marker genotype and gene frequencies at these polymorphic loci, the genetic structure of each breed population was analyzed, and the genetic variability within population was quantified, then the genetic relationships among breeds were determined. As for the marker gene and genotypes of each milk protein polymorphic locus, three genotypes, BB, BC and CC, controlled by two alleles (αS₁-CN^B and αS₁-CN^C) at αS₁-CN locus, tcn genotypes, A¹A¹, A¹A², A²A², A¹B, A²B, BB, A¹C, A²C. BC and CC, controlled by four alleles (β-CN^(A1), β-CN^(A2), β-CN^B and β-CN^C at β-CN locus, three genotypes. AA, AB and BB, controlled by two alleles (κ-CN^A and κ-CN^B) at κ-CN locus and three genotypes. AA, AB and BB. controlled by two alleles (β-LG^A and β-LG^B) at β-LG locus were identified among breeds. For the αS₁-CN locus the BB was the most common type (over 80%) in all three breeds. In the β-CN locus the prevalent genotypes were A²A²(65.8%) for Angus, A¹A²(35.6%) and A¹A¹(32.2%) for Hereford and A²A²(19. 3%), A¹B(19.3%), A²B(16.1%) and A²C(12.9%) for Charolais. At the κ-CN locus the highest frequency of the AA genotype(61.7 and 78.0% resp.) was observed in Angus and Hereford, whereas the BB genotype was extremely low. However, in Charolais the AB(38.7%) and BB(38.7%) genotypes were much more frequent than the AA genotype(22.6%). The most frequent genotypes at the β-LG locus were BB(63.9%) in Angus, AB(38.3%) and BB(35.1%) in Hereford and AA(50.0%) in Charolais. The most common casein(αS₁-, β- and κ-CN) genotype combinations(haplotype) in Angus, Hereford and Charolais were BB A²A² AA(33.0%), BB A¹A² AA (29.1%) and BB BA¹ AA(16.1%), respectively. In all breeds the frequency of the αS₁-CN^B gene ranging from 0.891 to 0.967 was overwhelmingly higher than that of the αS₁-CN^C gene. The highest gene frequency of β-CN locus was β-CN^(A2)(0.766) in Angus, β-CN^(A1)(0.511) in Hereford and β-CN^(A2)(0.371) and β-CN^B(0.306) in Charolais. Of the two genes in κ-CN locus the κ-CN^A gene(0.759 and 0.879 resp.) dominated in Angus and Hereford, while the κ-CN^B gene(0.581) was the most common in Charolais. In the β-LG locus the β-LG^B (0.797) and β-LG^A(0.641) genes were predominant in Angus and Charolais, respectively, whereas Hereford had an approximately equal distribution of β-LG^A(0.475) and β-LG^B(0.543). Significant differences between breeds were found at the gene frequencies of the β-CN, κ-CN and β-LG loci except for αS₁-CN locus. From the comparison of the data by measuring the average heterozygosity, effective numbers of alleles and gene homogeneity, the genetic variability within breed population was greatest for the Charolais, followed by the Hereford and Angus. In comparison of genetic identity, genetic distance and dendrogram calculated from the marker gene frequencies of milk protein polymorphic loci, the most close relationship was obtained between the Angus and Hereford and the lowest genetic similarity was obtained between the Angus and Charolais. And the Korean native cattle had close relationship with the Angus.