Schematic representation of the human IGH locus on chromosome 14q32.3. The IGH gene complex consists of numerous (>120) V gene segments, 27 D gene segments, 6 functional J gene segments, and C gene segments for the constant domains of the various IgH classes and subclasses, most of which are preceded by switch sequences (s).23,28,52 53 Pseudogenes are represented as open bars. The 27 Dh gene segments are grouped in 7 families based on sequence homology. Members of the same Dh family are depicted with the same shading pattern.