Summary of phylogenetic analyses of families including members on at least two of human Hox-bearing chromosomes (2, 7, 12, and 17), which indicated that one or more gene duplications occurred before the origin of vertebrates or after the mammalian radiation. For each family, the timing of duplications is indicated relative to a phylogeny of organisms, and the chromosomal locations of the corresponding human genes are indicated; e.g., the notation “CDK (12) (7,12,17)” indicates that a member of the CDK family on human chromosome 12 duplicated from the ancestor of other family members on human chromosomes 7, 12, and 17 before the divergence of fungi from animals. The bootstrap confidence level (BCL) for the internal branches of the phylogenetic trees are color-coded. The time window within which the vertebrate Hox clusters are believed to have duplicated is also indicated. Names of gene families are abbreviated as in Table 1.