Genetic maps of livestock based on molecular genetic markers provide tools for the detection and mapping of genes of economic importance in farm animals. The experimental designs employed for such studies are partly determined by the species characteristics or industry structure. Differences between designs include the number of generations studied, family structure e.g., half-sib or full-sib and the use of outbred lines or line-breed crosses. The appropriate method of analysis will depend on the design of the experiment. information required and assumptions which are valid on the underlying genetic model. An overview is given of the methods which are available for the detection of QTL. (C) 1997 Elsevier Science B.V.