Technical Abstract: The detection of genes affecting economically important traits in swine is a monumental task which requires a well designed plan to achieve its objective. The approach utilized by the Genome Mapping group at the USDA-ARS U.S. Meat Animal Research Center has four basic steps: 1) identify the region of the genome affecting the trait of interest through a genome-wide scan, 2) study the identified region in other populations and develop the comparative map, 3) select and test "positional candidate genes", and 4) sequence different alleles for the gene identified from animals of various breeds. To accomplish these goals, the swine mapping effort has developed a five generation resource population from a cross between Meishan and White composite swine. Traits which were measured related to reproduction, growth and carcass composition. To date, four genomic regions have been identified which affect carcass parameters and four regions have been identified for female reproduction. We are proceeding to step two for reproduction and carcass composition and finishing step one for growth characteristics.