ESTIMATION OF QTL EFFECTS FOR MILK-PRODUC TION TRAITS AND EXAMINATIONOF GENETIC-LINKAGE TO CASEIN MARKERS USING MULTIPOINT ANALYSIS

Marker assisted complex segregation analysis (MACSA) was applied to es timate the effects and position of a putative quantitative trait locus (QTL) of five milk production traits and protein to fat ratio based o n milk production performances of 1076 cows of Black Pied Dairy Cattle and Holstein Friesian as well as 645 cows of German Black and White. The genetic marker information of polymorphic milk proteins alpha(s1)- Casein, beta-Casein, kappa-Casein were used in a multipoint analysis e xaminating 3 marker-QTL-combinations. The QTL effects were estimated b y maximum likelihood method and were significant for 5 milk production traits but it was not for the protein to fat ratio. These results con firm the 'one marker analysis' results regarding QTL effects. The reco mbination rate suggests a medium linkage in case of the combination ka ppa-Casein-alpha(s1)-Casein-QTL which was significant for fat content (LOD score =3.03). Marker-QTL-combinations including beta-Casein show low recombination rates and indicate a close linkage especially regard ing fat yield, fat content and protein yield with LOD scores exceeding 1.