2. In this Chapter, We talked about how specific genes influence the development of species with novel shapes and forms. BUT HOW ABOUT HOW COMPLEX ORGANS COME TO EXISTENCE? This is still a major challenge for evolutionary biologists.
6. The Simple Eye Cont. Photoreceptor Cell Type of nerve cell Able to absorb light and respond to it Pigment cell Stops the light from going to the other side of the the Photoreceptor cell. Allows the organism to sense light and the direction it comes from. Primitive eyes give an organism an additional way to sense the environment. Might help avoid predators or locate food.
7. Eye Evolution Over time, eyes could be more complex by enhancing the ability to absorb different amounts of wavelengths. Since Darwin, evolutionary biologists have wrestled with the concept of eye evolution. This is because anatomically, researchers have discovered different types of eyes. Evolutionary Biologists Luitfried von Salvini-Plawen and Ernst Myer proposed that eyes might have independently arisen many times during evolution.
9. The Discovery of Pax6 Gene The protein encoded by Pax6 is a transcription factor that controls the expression of genes that are involved in the development of the eyes of rodents and humans. Mutation of Pax6 in Mice Small Eyes Mutation of Pax6 in Humans Aniridia Similarly the eyeless gene in flies (Drosophilia) control genes for its eye development. These genes are homologous
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12. Using genetic engineering techniques they were able to express the eyeless gene where the antennae should form.
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14. Also, when the Pax6 gene was expressed in the leg region, an eye was formed there also. Experiment Results
15. The Controversy Since the discovery of the eyeless and Pax6 gene, many other homologs of this gene have been discovered in many other species. Gehrig and his colleagues hypothesize with Darwin that all eyes do come from a common ancestral form . BUT, others argue that Pax6 only control certain features of eye development and different types of eyes may have evolved independently. More research still needs to be done.
