Phylogenetic tree of the cyclin-dependent kinase (CDK) family, constructed by the neighbor-joining method, on the basis of the proportion of amino acid difference (p). Numbers on the branches are the bootstrap confidence levels; only values ≥50% are shown. For genes on the human Hox-bearing chromosomes, chromosomal locations are indicated by circled numbers. Species included in the phylogeny are the following: Vertebrata: human (Homo sapiens), mouse (Mus musculus), chicken (Gallus gallus), clawed frog (Xenopus laevis), goldfish (Carassius auratus); Insecta: Drosophila melanogaster; Nematoda:Caenorhabditis elegans; Plantae: Arabidopsis thaliana, rice (Oryza sativa); Fungi: yeast (Saccharomyces cerevisiae), Schizosaccharomyces pombe, Kluyveromyces lactis.