Michael Syvanen and Jonathan Ducore. 2010. Whole genomoe comparrisons reveals a possible chimeric origin for a major metazoan assemblage. Journal of Biological Systems, Vol. 18, No. 2: 261–275
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Note: This paper is presented here with permission from "World Scientific Publishing Co. Pte. Ltd." They are the publisher and can be found at www.wspc.com.
Abstract: The availability of whole genome sequences from multiple metazoan phyla is making
it possible to determine their phylogeny. We have found that a sea urchin and human
define a clade that excludes a tunicate, contradicting both classical and recent molecular
studies that place the tunicate and vertebrate in the Chordate phylum. Intriguingly, by
means of a novel four taxa analysis, we have partitioned the 2000 proteins responsible
for this assignment into two groups. One group, containing about 40% of the proteins,
supports the classical assemblage of the tunicate with vertebrates, while the remaining
group places the tunicate outside of the chordate assemblage. The existence of these two
phylogenetic groups is robustly maintained in five, six and nine taxa analyses. These
results suggest that major horizontal gene transfer events occurred during the emergence
of one of the metazoan phyla. The simplest explanation is that the modern tunicate (as
represented by Ciona intestinalis) began as a hybrid between a primitive vertebrate and
some other organism, perhaps from an extinct and unidentified protostome phylum, at
a time close to but after the diversification of the chordates and echinoderms and before
the lineages leading to Drosophila melanogaster and Caenorhabditis elegans diverged.
Keywords: Horizontal Gene Transfer; Four-Taxa Analysis; Tunicate; Chordate; Protostome; Deuterostome.