From phenotype to genotype : towards positional cloning of QTL in livestock?

It is well established that QTL underlying economically important traits can be mapped in livestock using existing marker maps either in experimental crosses or outbred populations. The resolution that can be achieved using conventional designs, however, is usually insufficient for positional cloning of the corresponding genes. We briefly describe approaches to fine-map QTL with particular emphasis on an identity-by-descent (IBD) method that was successfully applied to locate a QTL influencing milk yield and composition in cattle within a 5 cM chromosome segment. Methodological options to go from a fine-mapped QTL to the identification of the actual genes and mutations are envisaged.