[Analysis of gene effects on performance characteristics].

In farm animals, associations between individually identified genotypes and the values of performance traits were investigated since more than 30 years. The topic of research was largely determined by the Veterinary Institute of the University of Göttingen. For the experimental analysis of gene loci, for which allelic variants are connected with alterations of trait values, new techniques of DNA diagnostic were of crucial significance. Thereby, two approaches of analysis of quantitative trait loci (QTL) can be distinguished. By considering informative groups of animals, the first approach uses marker loci in order to trace the inheritance of their alleles and thus simultaneously the transfer of specific chromosome sections to individuals of the offspring generation. By this manner, the associations between the marked chromosome regions and trait values are calculated. Results are shown for examples from experiments with milk performance in cattle and with fatting and carcass traits in pigs. In the second approach, genetic effects of trait values are assigned to distinct genes or gene clusters. For this purpose, variants of the gene structure are identified and then analysed for their effects on the formation of specific trait values. As an example of such a functional analysis of single gene positions, the milk protein coding genes in cattle are given. From the data we see that DNA techniques allow a direct access to genotypic information and so far-reaching potential for tracing back effects on trait values to single nucleotide differences. However, such a functional analysis need specific test systems which are able to consider the complex net work between single gene effects and the multifactorially caused values of performance traits. This will be possible by proceedings, which identify the gene effects in vivo and the balancing forces of haplotype combinations in populations. Genetic parameters of such investigations are needed for farm animal populations before variants of genotypes are applied for breeding.