Endocrine Abstracts

The cephalochordates (amphioxus) are the closest living invertebrate relatives of vertebrates, and have proved extremely useful for understanding the evolution of vertebrate genes and genomes. Molecular analysis in amphioxus has confirmed that vertebrates have a genome architecture that is fundamentally different from invertebrates. First, vertebrates have more genes than invertebrates. Second, vertebrates have many small multigene families (with 2 to 4 genes). Most of these are represented by single-copy genes in invertebrates, even in amphioxus. This pattern is clearly evident in the homeobox genes, but also extends to other gene types. Third, vertebrate genomes contain paralogy regions: large regions of chromosome that contain collections of genes, each with related genes mapping to another chromosome region. These data could be explained if the vertebrate genome had undergone two tetraploidy events during early chordate evolution. I will show data from the human genome and from the cephalochordate amphioxus that supports this hypothesis, and dates putative two tetraploidy events to the stem lineage of vertebrates. These findings have implications for with our understanding of animal complexity and for analyses of human genes.