Evolution Chapter 10- Guest Lecturer
Evolution Chapter 10- Guest Lecturer BIOL 3303
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This 24 page Class Notes was uploaded by Madeline Abuelafiya on Tuesday March 29, 2016. The Class Notes belongs to BIOL 3303 at Southern Methodist University taught by Dr. John Wise in Winter 2016. Since its upload, it has received 11 views. For similar materials see Evolution in Biology at Southern Methodist University.
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Date Created: 03/29/16
Chapter 10 Adaptation: from genes to traits Evolution of novel traits Complex adaptation (multiple loci, regulatory circuits and environmental aspects possibly involved). Barbara McClintock lDiscovery of Transposons lDemonstrated control genes have over physical characteristics. Gene duplication can produce novel functions Promiscuous proteins are especially likely to take on new functions after duplication lPotentiation: making the trait possible lActualization: making the trait manifest lRefinement: making the trait effective •A very powerful selective force comes from the interaction of living species. •Natural selection is not just interactions with the non- biological environment. 6 Hox Genes Vertebrate Hox genes These genes are paralogs clusters)genes in different What does a homeotic gene encode? Fly legs and mouse legs patterned by same genetic cascade OrthologousGenes Changes in limb patterning pathway resulted in snake limb loss •HoxC8/C6 expression in the anterior of snake prevents forelimb development •Less and less Shh expression led to loss of hind limbs Expression differences in a single gene give rise to limb elongation Change in expression of DppChange in expression of BMP2 These genes are orthologs (homologous genes separated in different species) Evolution of feathers – recycled signal networks •Placodes– disks of cells Tubular destinedto Scales Feathers be scales or feathers •Use of Shh and Bmp2 again Evolution of feathers Plumed Barbed Feathers Feathers Shh and Bmp2 used again –to form the rachis (central tube) and barbs Complex eyes have evolved in several lineages •The particular molecules usedfor crystallinsand opsins are different! –C-opsins in vertebrates –R-opsins in invertebrates •Different lineages Opsins evolved from serpentine proteins GPCR (G-protein coupled receptors) Crystallins evolved through gene recruitment Hypothesis for evolution of the vertebrate eye Evolution of the Mollusk Eye The different eye forms found in mollusks are shown to the right. May be analogousto an evolutionary pathway from a simple light absorbing pigment to a complex camera-like eye. (a) Pigment spot (b) pigment cup (c) optic Littorina and octopusplex lensedeye of Constraints on adaptation •Laws of physics •Pleiotropy –Single gene affects traitssion of many Antagonistic pleiotropy: number of cervical vertebrae Children born with an abnormal number of cervical vertebrae – –More likely to be stillborn –120 times more likely to have pediatric cancers Antagonistic pleiotropy Complex adaptations are often imperfect Recurrentlaryngeal nerve is a “stupid” design Evolutionoperatesin the short term, with each step taking place as a modification ofwhatis already present Evolutiontinkers with what exists... Convergent evolution in mammals •Physics sets the parameters •Biology fills the niche starting from wherever it starts Convergent evolution in mammals •Placental relative of a cat, Smilodon •Marsupial relative of an opposum, Thylacosmilus
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