Human cells obtained either from individuals with certain genetic disorders or from apparently normal individuals will be cultured and studied cytogenetically, immunologically, biochemically, and with respect to growth in vitro. In addition, correlations of clinical with laboratory findings will be made. Some studies will be clinical investigation, while others will be basic laboratory experimentation using human cells. Specific research areas, in addition to karyotype-phenotype correlations, include: assignment of genes to specific chromosome regions; the established sequences in which the chromosomes replicate; the phenomenon of chromatid exchange; several aspects of Bloom's syndrome.