Schematic phylogenies of families having members on all fourHox-bearing chromosomes that duplicated early in vertebrate history: (a) Hox clusters (Zhang and Nei 1996); (b) collagen genes (Bailey et al. 1997); (c) ERBB family; (d) phylogeny consistent with the phylogenies of most three-member families (Fig. 5). Numbers on the branches are the bootstrap confidence levels; only values ≥50% are shown. Chromosomal locations are indicated by circled numbers.