Figure 6.

A model for the evolution of the vertebrate Dlx gene family. This model is based on the phylogenetic tree shown in Fig. 3 and on the linkage relationships of gnathostome Dlx and Hox genes (8). We propose that a tandem duplication of an ancestral Dlx gene predated the divergence of lampreys from gnathostomes, which was followed by independent chromosomal or genome duplications and gene loss in each lineage. Dlx and Hox linkage are currently unknown in lampreys. Asterisks indicate uncertain linkage relationships.