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The Simple Life Ain't So Simple

6 December 2005 (All day)
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Trends in Genetics

Complicated.
The Nematostella vectensis anemone has a more complex genome than previously thought.

The anthropomorphic view of evolution just received another blow. Humans top the evolutionary hierarchy because of our supposed complexity, which is backed by an incredibly sophisticated genetic portfolio. But a new survey of marine life indicates that "simple" organisms such as corals and sea anemones have many of the same genes and complex gene families--consisting of many closely related genes derived from the same ancestral gene--as we do, leaving open the question of what really sets us apart from other species.

It stands to reason that the more genetically complex an organism is, the loftier its place on the evolutionary tree. And indeed, genome comparisons of mammals to model organisms such as fruit flies and nematodes reveal that humans typically have larger families of related genes than these lower life forms. Geneticists think such related genes evolved slightly different functions over time, making us what we are today.

But the story may not be that simple. When Ulrich Technau, a molecular biologist at the University of Bergen, Norway, and colleagues conducted a survey of 17,000 expressed sequence tags--pieces of genes yanked from DNA sequence--they found that cnidarians such as coral and sea anemones have similar genetic underpinnings to vertebrates, be they fish or people. Cnidarians share extended gene families with vertebrates that fruit flies and nematodes lack, suggesting that insects and worms lost many members of those families. Indeed, the data hint that cnidarians have more genes than either fruit flies or nematodes. To date, Ulrich's group, which reports its findings in this month's issue of Trends in Genetics, has found 318 genes in the sea anemone and 196 in the coral that coincide with vertebrate genes but don't exist in ecdysozoan, the group that includes fruit flies and worms.

"The genomic complexity of ... cnidarians is much greater than expected," says John Finnerty, an evolutionary biologist at Boston University. "There is no simple relationship between the numbers of genes an animal possess and its complexity at the morphological level."

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