ANALYSIS OF GENE EFFECTS ON PERFORMANCE T RAITS

In farm animals, associations between individually identified genotype s and the values of performance traits were investigated since more th an 30 years. The topic of research was largely determined by the Veter inary Institute of the University of Gottingen. For the experimental a nalysis of gene loci, for which allelic variants are connected with al terations of trait values, new techniques of DNA diagnostic were of cr ucial significance, Thereby, two approaches of analysis of quantitativ e trait loci (QTL) can be distinguished, By considering informative gr oups 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 gener ation. By this manner, the associations between the marked chromosome regions and trait values are calculated. Results are shown for example s from experiments with milk performance in cattle and with fatting an d carcass traits in pigs. In the second approach, genetic effects of t rait values are assigned to distinct genes or gene clusters. For this purpose, variants of the gene structure are identified and then analys ed for their effects on the formation of specific trait values. As an example of such a functional analysis of single gene positions, the mi lk 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 sin gle nucleotide differences. However, such a functional analysis need s pecific test systems which are able to consider the complex net work b etween single gene effects and the multifactorially caused values of p erformance traits. This will be possible by proceedings, which identif y the gene effects in vivo and the balancing forces of haplotype combi nations in populations. Genetic parameters of such investigations are needed for farm animal populations before variants of genotypes are ap plied for breeding.