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Friday, 8 February, 2002, 10:20 GMT
Simple error means big change
Do the genes in Artemia tell us how evolution works?
By BBC News Online science editor Dr David Whitehouse

Biologists have uncovered important genetic evidence about how evolution redesigns animals.

This may establish how relatives of this gene in many, many different organisms might actually work

Michael Ronshaugen, UCSD
It explains how large-scale changes to body plans can arise from very simple genetic mutations, or errors.

The scientists say these mutations occur in regulatory genes that control embryonic development. They believe such "mistakes" would have caused crustaceans with limbs on every segment of their bodies to evolve 400 million years ago into a radically different shape: six-legged insects, and then into other types of animals.

The researchers claim the discovery answers a major criticism creationists have levelled against evolution - that there is no genetic mechanism that could permit animals to produce radical new body plans.

How evolution works

"The problem for a long time has been over this issue of macroevolution," said Professor William McGinnis of the University of California at San Diego, US.

"How can evolution introduce big changes in an animal's body shape and still generate a living animal? Creationists have argued that any big jump would result in a dead animal that wouldn't be able to perpetuate itself.

"Until now, no one's been able to demonstrate how you could do that at the genetic level with specific instructions in the genome."

Writing in the journal Nature, the researchers show that this could be accomplished with relatively simple mutations in a class of regulatory genes, known as Hox. These act as master switches by turning on and off other genes during embryonic development.

New insights

Using fruit flies and a crustacean known as Artemia, or brine shrimp, the scientists showed how modifications in the Hox gene known as Ubx would have allowed the ancestors of Artemia, with limbs on every segment, to lose their hind legs and become six-legged insects.

Fly, BBC
Fruit flies are regularly used to test genetic theories
"The change in the mutated protein [produced from UBx] allows it to turn off other genes," said Professor McGinnis, who discovered in 1983 that the same genes work in all animals, including humans.

"Before the evolution of insects, the genes responsible for leg formation didn't get turned off.

"But during the early evolution of insects, this gene and the protein it encoded changed so that they now turned off those genes required to make legs, essentially removing those legs from what would be the abdomen in insects."

Explaining some cancers

The discovery of the general mechanism for producing major leaps in evolutionary change has implications for other scientists.

It may provide biologists with insights into the roles of other regulatory genes involved in more evolutionarily recent changes in body designs. In addition, the discovery of how this particular Hox gene regulates limb development may also have an application in improving the understanding of human disease and genetic deformities.

According to Michael Ronshaugen, also of UCSD: "This may establish how relatives of this gene in many, many different organisms might actually work.

"A lot of these genes are involved in the development of cancers and many different genetic abnormalities and they may explain how some of these conditions came to be."

See also:

09 May 01 | Sci/Tech
Climate change aids evolution
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