Thirty-one individuals have been identified as having a recombinant chromosome 8 (rec 8) secondary to a parental pericentric inversion of chromosome 8 (inv 8). In all cases, the rec 8 has been associated with a highly specific phenotype, including developmental delay. All people with either rec 8 or inv 8 have the same breakpoints and have been of Hispanic descent, with ancestors coming from Northern New Mexico/Southern Colorado. Because of this common heritage and the presence of an inv 8 chromosome in one parent for each individual with the rec 8, a common ancestor is postulated. Extended family pedigrees with subsequent cytogenetic analysis when appropriate, and complete medical and developmental evaluation of individuals with the rec 8 would allow us to meet the following project goals: 1. Identify all rec 8 patients and inv 8 carriers to establish risk and prevalence data. 2. Define both the inv 8 and rec 8 phenotypes at the clinical and cytogenetic levels. 3. Provide family counseling and plan for appropriate medical care. 4. Develop a framework for educating health care providers and the public regarding the significance of this chromosome abnormality. 5. Use cytogenetic findings as a tool for clarifying the ethnohistorical origins of the Hispanic population in the Southwestern United States. The scientific disciplines involved include clinical genetics, pediatrics, cytogenetics, anthropology, education, and population genetics.