The genetic epidemiology study will build improved highly-precise sex-specific linkage maps utilizing thousands of individuals who have previously been genotyped. After filtering out obvious relationship and genotype errors, the study will incorporate methods that properly model for genotyping errors. In addition to creating precise maps for the scientific community, the study will also use these genotype data to study how recombination may vary between ethnic groups. The genotypes generated by the NHLBI Mammalian Genotyping Service are precisely the type of data required to produce more accurate maps. These data collections contain over 3,400 pedigrees with more than a 100-fold increase in information compared to that contained in the 8 CEPH families that have been used to construct current genome-wide linkage maps. The new maps will be made publicly available and the genotype data from the study will be accessible by the MAP-0-MAT linkage mapping server. In the future, the study will be broadened to incorporate genotype data from additional genotyping centers such as the Center for Inherited Disease Research (CIDR).