Speciation

And then change relatively little for the rest of

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Unformatted text preview: tle for the rest of their existence little Time Is this due to periodic selection? How did whales evolve? Evolutionary novelties may arise in several ways Evolutionary Many complex structures evolve in many stages • From simpler versions having the same basic function Light-sensitive cells Light-sensitive cells Fluid-filled cavity Transparent protective tissue (cornea) Cornea Lens Layer of light-sensitive cells (retina) Optic nerve Eyecup Nerve fibers Nerve fibers Patch of lightsensitive cells Limpet Optic nerve Eyecup Abalone Retina Optic nerve Simple pinhole camera-type eye Eye with primitive lens Complex camera-type eye Nautilus Marine snail Squid Novel structures result from exaptation • The gradual adaptation of existing structures to The new functions new Genes that control development are important in evolution important “Evo-devo” • Is a field that combines evolutionary and Is developmental biology developmental THE GENETIC CONTROL OF THE EMBRYONIC DEVELOPMENT EMBRYONIC Cascades of gene expression and cell-to-cell Cascades signaling direct the development of an animal signaling Early understanding of the relationship between Early gene expression and embryonic development gene • Came from studies of mutants of the fruit fly Came Drosophila melanogaster Drosophila Eye Antenna SEM 50× Head of a normal fruit fly Leg Head of a developmental mutant A cascade of gene cascade expression expression • Controls the Contro...
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This document was uploaded on 02/26/2014 for the course ENG 102 at Maryland.

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