Research focused on a group of genes that control how and where body parts develop in animals, including people, reveals the genetic potential to create fingers and toes apparently existed ages before animals even crawled onto land.
Scientists investigated the activity of these "Hox genes" in embryos of the spotted catshark and discovered the gene dates back to the distant common ancestors of sharks and humans.
Unexpectedly, they discovered that a spurt of genetic activity that helps digits such as fingers and toes develop in limbed animals was seen in shark embryos as well.
"Genetic processes were not simple in early aquatic vertebrates only to become more complex as the animals adapted to terrestrial living. They were complex from the outset," said developmental biologist Martin Cohn at the University of Florida at Gainesville.
Although the genetic program needed to create digits might exist in sharks and many other kinds of fish, they only activate it briefly, said University of Florida graduate students Renata Freitas and Guangjun Zhang.
Humans and other land animals ultimately descend from bony fish.
Sharks, on the other hand, possess skeletons made of cartilage, not bone. This suggests the genetic potential for fingers and toes existed more than 500 million years ago, in the last common ancestor of bony and cartilaginous fish.
These findings might not only shed light on the evolution of animals on Earth, but also could provide insights on ways to cure human birth defects, which affect about 150,000 infants annually in the United States.
For instance, when a particular Hox gene is mutated in humans, "it results in malformations of fingers and toes," Cohn said.
Source:Xinhua/agencies
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