Inbreeding

Inbred populations can offer a rich resource for genetic studies. They have the advantage of often being relatively homogeneous in both their genetics and environment. A method that has been used successfully to identify several recessive mutations in inbred groups is homozygosity mapping.

This approach looks for regions of alleles at genetic loci that are linked to one another and are homozygous. With inbreeding, there is an increased chance that, in an affected individual, the two alleles at the disease locus will have descended from a common ancestor. Therefore tightly linked markers (identifiable DNA segments) surrounding the disease locus will also tend to come from the same ancestral chromosome and thus be identical on both homologous chromosomes.

Together with colleagues, Erik Puffenberger, a research scientist and laboratory director at the Clinic for Special Children in Strasburg, Pennsylvania, capitalized on the inbreeding in a large Mennonite kindred to identify the location of a gene for Hirschprung disease on chromosome 13. In this family, parents of an affected child are, on average, related as closely as second or third cousins. The region was located because, true to theory, affected individuals shared alleles that were identical by descent at the region containing the disease gene.