Aktueller stand und perspektiven der molekularen tierzucht

The adjective "molecular" in "molecular animal breeding" refers to the DNA molecule, the biochemical basis of inheritance. Selection involving molecular information (like conventional selection) does not modify the DNA molecule but the frequencies of naturally occurring DNA-variants (alleles). The quantitative genetic model of animal breeding assumes allelic variation at a very large number of loci (polygenes) to cause the genetic component of the phenotypic variation. Theoretically, the effects of individual polygenes are too small to be detected. However, so called major genes were identified in swine, cattle and sheep due to their relatively large effects and elaborated phenotypic analyses. A prominent example is the "halothane gene" in swine. The allelic variants of most major genes have been characterized at the molecular level. Application of the "molecular halothane test" allowed efficient selection against the porcine stress syndrome and contributed significantly to the improvement of pork quality within the last decade. Molecular markers allow the analysis of segregation at loci with relatively small effects on the variation of a quantitative trait, so called quantitative trait loci (QTL). QTL have been identified in all farm animal species. Markers linked to the QTL can be utilized in marker assisted selection (MAS) schemes. However, the use of linked markers will be gradually replaced by selection directly based on the knowledge of DNA variants that are responsible for the QTL variation. A first example is the molecular characterization of a QTL affecting milk composition characteristics. Molecular QTL information allows for decomposing the breeding value in a QTL and a polygenic component and thereby enables a higher accuracy and efficiency of selection. The "QTL model" and the "polygenic model" are not mutually exclusive. Thus, conventional animal breeding will not be replaced by molecular animal breeding but complemented.