This thesis is an investigation of the genes underlying economically important traits in pigs. A radiation hybrid map of porcine chromosome 9 (SSC9) was constructed, and a number of polymorphic markers were identified and genotyped by PCR-RFLP methodology. These markers, along with previously genotyped polymorphisms on SSC3 and SSC6 were analyzed for associations with litter size in a Meishan x Large White resource population. Five suggestive associations (P <= 0.10) and one significant association (P <= 0.05) were found. Based on published reports, a variety of candidate genes for meat and carcass quality traits were evaluated in a multibreed resource population, including FABP3, FABP4, FABP5, LEPTIN, MYF3, MY0G and MC4R. DNA was extracted from a total of 182 gilts, genotyped by PCR-RFLP, and each locus was analyzed for associations with over fifty phenotypic traits. Fifty-four significant associations between the marker loci and tested traits were found (P <= 0.05).