Abstract
Cosmid clones containing the human .gamma., .epsilon. and .alpha. H chain constant region genes and an .epsilon. pseudogene were isolated. All these genes have a switch sequence detectable by hybridization. Overlapping cosmids covering 2 separate regions of the genome were studied, and the gene order in each of these regions was found to be .gamma.-.gamma.-.epsilon.-.alpha.. This implies an evolutionary duplication in this multigene family involving .gamma., .epsilon. and .alpha. genes.