The animal in the genome: comparative genomics and evolution.

Comparisons between completely sequenced metazoan genomes have generally emphasized how similar their encoded protein content is, even when the comparison is between phyla. Given the manifest differences between phyla and, in particular, intuitive notions that some animals are more complex than others, this creates something of a paradox. Simplistic explanations have included arguments such as increased numbers of genes; greater numbers of protein products produced through alternative splicing; increased numbers of regulatory non-coding RNAs and increased complexity of the cis-regulatory code. An obvious value of complete genome sequences lies in their ability to provide us with inventories of such components. I examine progress being made in linking genome content to the pattern of animal evolution, and argue that the gap between genomic and phenotypic complexity can only be understood through the totality of interacting components.