Inner Fish Chapter 3 Summary

     Chap. 3, "Handy Genes," was about DNA, genes, embryonic development and what parts of these genes are turned on or off to make parts of a body such as limbs in the embryonic development stages. Sequences of DNA make us who we are. Shubin's lab is separated into two parts: a section for fossils and a section devoted to DNA. While Shubin was in the Arctic, another researcher was working in his lab shooting vitamin A into skate and shark embryos. Our body knows how to develop because of the concentration of chemicals produced by the cells. All the genetic switches that control this do their thing between the third and eighth week after conception. Certain patches of cells were responsible for all limb development. Remove that patch and no limb develops. Turn the patch cells over and the limb grows backwards. Cut the patch in half and you have two limbs. Later scientists did an experiment involving flies and found a gene called hedgehog. This gene controlled which end of the fly was which. They looked for this in other creatures and found the hedgehog gene to be in many other organisms. They named the chicken version of the gene Sonic Hedgehog. It was found to be only active in the patches that control limb development. The form of Vitamin A caused the Sonic Hedgehog to activate. Every living organism with limbs has the sonic hedgehog gene. The vitamin A even caused mirror limbs to sharks and skates. Then the scientist injected mouse protein and the shark limb was affected the way it was with vitamin A injections. This means that the mouse and shark genes are similar proving the concept of common ancestor.