Invertebrates 2

Invertebrates 2 - Evo-Devo or the study of the evolution of...

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1 „Evo-Devo‟ or the study of the evolution of development Q. Why study this? A. Development is the process that gives rise to form , and so the evolution of form is brought about through the evolution of development. 1. All animals have the same basic genetic „toolkit‟ – the genes responsible for building bodies and body parts are shared by virtually all animals Humans have just 14 more genes than chimps 2. Many animal „toolkit‟ proteins exhibit functionally equivalent activity in vivo when substituted for one another Halder et al 1995 Observed that mammals and insects, which have evolved separately for more than 500 million years, share the same master control gene for eye morphogenesis So how does morphological diversity evolve? Consider a species that exists in different forms, the forms can be more distinct in terms of morphology and ecology than the adult forms of any pair of sister species Drosophila melanogaster life cycle D. melanogaster D. simulans So the Drosophila is using the identical set of toolkit proteins to create markedly different body morphologies. Achieved by regulating which genes are expressed and by when, where and how much they‟re expressed. The Genetic Theory of Morphological Evolution Proposed by Sean Carroll of U. of Wisconsin (interview on pages 534-535). 1. Form evolves largely by altering the expression of functionally conserved proteins, and 2. Such changes largely occur through mutations in the promoter sequences of the regulatory genes and their target genes that participate in developmental pathways Figure 17.3b, page 329
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2 Fig. 18.8, page359 nGAAnGAAnGAAnGAAnGAA Cis -regulatory element, eg. heat shock element Transcription factor is a protein that binds to specific sequences of DNA (the Cis - regulatory elements) to control the transcription of genetic information from DNA to RNA The genetic theory of morphological evolution proposes that gain, loss, or modification of sequences in these promoter and other regulatory control regions of genes is the predominant mechanism underlying evolution of development and form Regulatory divergence modifies limb length between mammals, Cretekos et al, 2008 Prx1 RNA expression in the developing forelimb Gene named Prx1 is involved in limb formation Scientists replaced the promoter of the mouse Prx1 gene with the promoter of the fruit bat Prx1 gene Promoters shared 94% similarity Resulting mice had longer limbs than usual Suggests that bat wings may have arisen through changes in promoter sequence Promoter Gene Mouse +/+ Bat BatE/BatE Competing theory Greg Wray and Jerry Coyne Mutations in the coding regions of genes (the sequence that translates to protein) provide the mechanism for natural selection and evolution of form
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3 Genetic analysis of cavefish reveals molecular convergence in the evolution of albinism. Protas et al, 2006.
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This note was uploaded on 03/22/2010 for the course BISC 120 taught by Professor Webb,wetzer,? during the Fall '07 term at USC.

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Invertebrates 2 - Evo-Devo or the study of the evolution of...

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