Increasing genomic complexity by gene duplication and the origin of vertebrates

Prevailing hypotheses concerning the origin of the vertebrate genome postulate successive genome duplications before the origin of fishes or tetrapods. These hypotheses predict episodic expansion of gene families early in vertebrate evolution (mostly before the origin of fishes), tetralogous relationships between gene copies samples from invertebrates and vertebrates, and gene family trees with symmetrical shapes. None of these predictions were evident from a phylogenetic analysis of 35 gene families. Overall, the results do not refute the hypothesis that gene family evolution is governed by independent gene duplications occurring with identical probability across gene lineages. These results suggest that the genome complexity of contemporary vertebrates mostly reflect small-scale (regional) DNA duplications instead of large-scale (genomic) duplications.