rav65819_ch25_489-502

rav65819_ch25_489-502 - ;;;;;;;; 25 chapter Evolution of...

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Unformatted text preview: ;;;;;;;; 25 chapter Evolution of Development introduction HOW IS IT THAT CLOSELY related species of frogs can have completely different patterns of development? One frog goes from fertilized egg to adult frog with no intermediate tadpole stage. The sister species has an extra developmental stage neatly slipped in between early development and the formation of limbsthe tadpole stage. The answer to this and other such evolutionary differences in development that yield novel phenotypes are now being investigated with modern genetic and genomic tools. Research findings are accentuating the biological paradox that many developmental genes are highly conserved, and a tremendous diversity of life shares this basic toolkit of developmental genes. In this chapter, we explore the emerging field of developmental evolution, a field that brings together previously distinct fields of biology. 25.5 Gene Duplication and Divergence Gene duplications of paleoAP3 led to owering-plant morphology Gene divergence of AP3 altered function to control petal development concept outline 25.1 The Evolutionary Paradox of Development Highly conserved genes produce diverse morphologies Developmental mechanisms exhibit evolutionary change 25.2 One or Two Gene Mutations, New Form Cauli ower and broccoli began with a stop codon Cichlid sh jaws demonstrate morphological diversity f 25.3 Same Gene, New Function Ancestral genes may be co-opted for new functions Limbs have developed through modi cation of transcriptional regulation f 25.4 Different Genes, Convergent Function Insect wing patterns demonstrate homoplastic convergence Flower shapes have also altered in a convergent way 25.6 Functional Analysis of Genes Across Species 25.7 Diversity of Eyes in the Natural World: A Case Study Morphological evidence indicates eyes evolved at least twenty times The same gene, Pax6, initiates y and mouse eye development Ribbon worms, but not planaria, use Pax6 for eye development The initiation of eye development may have evolved just once 489 rav65819_ch25_489-502.indd 489 rav65819_ch25_489-502.indd 489 11/27/06 1:48:00 PM 11/27/06 1:48:00 PM 25.1 The Evolutionary Paradox of Development Ultimately, to explain the differences that occur among species, we need to look at changes in developmental processes. That is, changes in genes have their effects by altering development, thus producing a different phenotype. Phenotypic diversity could either result from many different genes or the differences could be explained by how a smaller set of genes are deployed and regulated. Based on our current understanding of the evolution of new phenotypes, the latter explanation is most probable....
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rav65819_ch25_489-502 - ;;;;;;;; 25 chapter Evolution of...

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