Schematic map of the mouse and human IgH genetic cluster. The IgH cluster and the closest genes (dark blue) are highly conserved in the mouse and human chromosomes. The same transcription direction was also detected in both species, with a "telomere towards centromere" transcription versus. The mouse IgH cluster harbors 8 constant genes and one copy of the 3' Regulatory Region (3'RR) with 7 enhancers, 3 of them (HS5, HS6, HS7) with possible insulator function at the 3' boundary of the cluster. The human IgH region has some differences for the constant genes since a wide duplication of gamma, epsilon and alpha genes occurred in the ancestor of Hominoidea. This duplication included also the 3'RR at the 3' of the constant alpha gene. Both the two copies of the 3'RR in humans have just three enhancers. In fact, the human loci do not harbor both the duplicated HS3.B enhancer and the insulators present in the mouse locus.
D'Addabbo et al. BMC Evolutionary Biology 2011 11:71 doi:10.1186/1471-2148-11-71