Evolutionary Genomics for Eye Diversification
There are several types of eyes in morphology such as camera eye, compound eye, mirror eye, and single lens eye, and all the eye types have been evolved from the same origin, the prototype eye. Even though there are conserved genes and networks in the eye
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Evolutionary Genomics for Eye Diversification Atsushi Ogura
Abstract There are several types of eyes in morphology such as camera eye, compound eye, mirror eye, and single lens eye, and all the eye types have been evolved from the same origin, the prototype eye. Even though there are conserved genes and networks in the eye evolution, little is known about what kinds of genetic basis have been contributed to the eye diversification. It is essential for discovering genes for the morphological diversification to develop a platform of genomic and transcriptomic comparison among species. We, therefore, developed microarray that cover the genes related to development, function, and structure of molluscan eye, as an example, for the evolutionary genomic studies.
11.1
Evolutionary Genomics for Eye Diversification
11.1.1 Evolution of the Eye The eye is one of the most elaborate organs in animals and the study of its evolution is of particular interest. The evolution of animal eyes has been one of the most fundamental and classical subjects in the field of biology dating back to the time of Darwin. However, it has been difficult to understand how this complex organ arose simply from mutations and selections. Darwin discussed this matter in his “On the Origin of Species by Means of Natural Selection” in a chapter titled, “Difficulties of the Theory”, in which he wrote that “organs of extreme perfection and complication” such as the eye remained inexplicable by his theory (Darwin 1859).
A. Ogura Division of Advanced Sciences, Ochadai Academic Production, Ochanomizu University, Ohtsuka 2-1-1, Bunkyo, Tokyo 112-8610, Japan e-mail: [email protected]
P. Pontarotti (ed.), Evolutionary Biology – Concepts, Molecular and Morphological Evolution, DOI 10.1007/978-3-642-12340-5_11, # Springer-Verlag Berlin Heidelberg 2010
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A. Ogura
The evolutionary study of animal eyes was also difficult for a long time from the viewpoint of molecular evolution and biology. There were only a few molecular theories to link primitive eyes to the elaborate and varied eye organs commonly seen today. It seemed that natural selection could not adequately explain the evolutionary mechanism underlying the development of complex animal eyes. However, studies based on basic control genes in the developmental processes in animal eyes have revealed that there is a conserved key regulatory network represented by the Pax6 genes among almost all animals (Gehring 1996; Fernald 2000). Even though there are no clear evolutionary tracks between the various types of animal eyes, the evolutionary history of the eye can be explained from the conserved molecular mechanisms. Recent studies have also reported that not only the core gene regulatory network for eye development but also genes downstream of the network and other peripheral genes related to the function and structure of eyes have been conserved among animals at least since the split of bilateral animals (Box 11.1). The origin and ancestral prototype of the eye as well as the molecular mechani
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