In order to determine when fish sprouted feet and started walking on land, a group of researchers have decoded the genome of the coelacanth, "a prehistoric-looking fish whose form closely resembles those seen in the fossils of 400 million years ago"
Dr. Amemiyas team has sifted through the coelacanths genome for genes that might have helped its cousin species, the ancestor to the first tetrapod, invade dry land some 400 million years ago. They have found one gene that is related to those that, in animal species, build the placenta. Coelacanths have no placenta, but they produce extremely large eggs, with a good blood supply, that hatch inside the mothers body. This gene could have been developed by land animals into a way of constructing the placenta.
Another helpful preadaptation is a snippet of DNA that enhances the activity of the genes that drive the formation of limbs in the embryo. The Amemiya team focused on the enhancer DNA sequence because it occurred in the coelacanth and animals but not in ordinary fish. They then inserted the coelacanth enhancer DNA into mice.
It lit up right away and made an almost normal limb, said Neil Shubin, meaning that the coelacanth gene enhancer successfully encouraged the mouse genes to make a limb. Dr. Shubin, a member of the team, is a paleontologist at the University of Chicago.
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