Fig. 5. Chromosome evolution in metazoan lineages.

Phylogenetic distribution of chromosome changes in (A) early bilaterian-cnidarian-sponge divergence, (B) spiralians, (C) cnidarians, and (D) chordates. All ancestral states and changes are inferred from genome comparisons and reconstructions as described in the text. ALGs not shown on branches retain ancestral state. Algebraic symbols are defined in Fig. 4 and in the text. Blue starbursts represent whole-genome duplications. Note that prior rearrangements in the indicated ancestor are denoted in shorthand, e.g., A1bB3 represents the cnidarian ancestral state A1b⊗B3 and B1B2 represents B1⊗B2.