Figure 1.

A. Phylogeny of gnathostome (jawed) vertebrates. The tree shows evolutionary relationships among cartilaginous fish and other major vertebrate lineages. The time scale is in million of years from the present for estimated divergence times [17,70]. The gray bars at the nodes indicate estimated intervals of divergence times for the extant subclasses of cartilaginous fish, Elasmobranchii and Holocephali, the orders Selachii (sharks) and Batoidea (skates, rays), and in the order Chimaeriformes the families Callorhinchidae (Callorhincus milii, elephant fish), Chimaeridae (Hydrolagus colliei, spotted ratfish). B. Arrangement of gene segments at an Igμ cluster. GL organization of VH, D1, D2, and JH gene segments flanked by RSS. Average distance between gene segments is about 400 bp, as indicated. Signal sequence and gene segments are labeled, filled triangles indicate RSS with 23 bp spacers, open triangles those with 12 bp spacers.