Posted on 12/13/2002 8:04:31 AM PST by Right Wing Professor
The first chordates appear in the fossil record at the time of the Cambrian explosion, nearly 550 million years ago. The modern ascidian tadpole represents a plausible approximation to these ancestral chordates. To illuminate the origins of chordate and vertebrates, we generated a draft of the protein-coding portion of the genome of the most studied ascidian, Ciona intestinalis. The Ciona genome contains ~16,000 protein-coding genes, similar to the number in other invertebrates, but only half that found in vertebrates. Vertebrate gene families are typically found in simplified form in Ciona, suggesting that ascidians contain the basic ancestral complement of genes involved in cell signaling and development. The ascidian genome has also acquired a number of lineage-specific innovations, including a group of genes engaged in cellulose metabolism that are related to those in bacteria and fungi.
This is an important genome; Ciona is a seasquirt, a chordate (the phylum that includes humans) but it is obviously not a vertebrate. It diverged from the main line of human evolution about 550 million years ago. Note that this organism, whose adult appearance and niche is very similar to that of other sedentary marine invertebrates, has a genome which contains simplified versions of vertebrate genes.
No. You're thinking of the Echinoderms.
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