Organization of the Atlantic salmon duplicated IgH loci. The sequences in the two IgH loci containing VH and CH regions cover approximately 670 kb (IGH-A) and 710 kb (IGH-B), respectively. The positions of the small gaps are indicated by triangles (IGH-A gap at position 760.2 kb; IGH-B gaps at position 282.8 kb, 372.8 kb and 555.4 kb). The numbers near VH genes indicate the VH genes family numbers. Transcriptional directions for the CH genes are shown by arrowheads. A numerated version of Figure 1 is available in Additional file 1 (IGH-A) and Additional file 2 (IGH-B).