DNA-based markers and genetic maps of major livestock species have been developed in the last few years. These, together with experimental populations and appropriate statistical methods, provide the tools to dissect causes of economically important genetic variation in livestock. A cross between genetically diverse lines is a powerful experimental design for such a study. In an F2 or backcross population from such a cross, markers are likely to be highly informative and the genes that control the differences between the lines will be segregating. We have been developing such a resource population based on a cross between the British Large White and Chinese Meishan pigs. These breeds differ for many traits, with the Meishan being inferior for growth rate and fatness, but superior for reproduction traits. Here we report the mapping of major genetic effects on growth rate and fatness in our cross.