Frog builds toes, then legs | Science News


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Frog builds toes, then legs

Watching gene activity of growing coquí frogs reveals surprising sequence

10:04am, July 9, 2008

A small frog appears to jump-start its skeletal development, turning on genes for building feet and toes before bothering to build its legs.

While researchers are still trying to figure out how a clump of cells becomes a wing or flipper or arm, the order of events has been established: The upper arm bone forms first, then the forearm, then the wrist bones, and finally fingers or toes.

But the new research, reported in the July–August Evolution & Development, hints that limb formation may not be so clear-cut.

“This is a very interesting idea,” says developmental geneticist Francesca Mariani, who was not involved with the research. “Maybe limb development has different ways of occurring.”

The evolutionary pathway from ancient fish fins to the structures that today’s creatures use for flying, burrowing, running and jumping has long intrigued scientists

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