Homology/Analogy Natalia Alvarez Kevin Coleman 2006 Botany 940 Evidence for evolution

  • View
    212

  • Download
    0

Embed Size (px)

Text of Homology/Analogy Natalia Alvarez Kevin Coleman 2006 Botany 940 Evidence for evolution

  • Homology/AnalogyNatalia AlvarezKevin Coleman2006Botany 940Evidence for evolution

  • Homolog structure: Similar structure and position, but different function

    Courtesy of Prof. Ken Sytsmahttp://evolution.berkeley.eduAnalog structure: Similar function, but different origin

  • HomologyHow can we explain this?

    Hypotheses??Courtesy of Prof. Ken Sytsma

  • HomologyArchetypal explanationThe same organ in different animals under every variety of form and function. (Owen,1843)Common ancestryA structure is similar among related organisms because those organisms have all descended from a common ancestor that had an equivalent trait. (Darwin,1859)

    Homology in character evolution. Staton, July 2000

  • Wells Critique: Circular definitionHomology/Common ancestorFeatures are homologous because they are inherited from a common ancestorCommon ancestry is inferred using homologous features.

    Features can be tested by Multiple ad hoc hypothesis of homology (Kluge 1997)Origin of arthropod compound eye. Oakley,2002.

  • How would you test common ancestry?

  • How would you test common ancestry?Fossil recordStructure and positionbehavioral patterns

  • Fossil record-Fossil intermediatesBehavioral patternsDinosaurBirdAlligator

  • How would you test common ancestry?Fossil recordStructure and positionbehavioral patternsGenetics

  • Wells Critique: GeneticsAssumption: homologous features are programmed by similar genesProblems1. Similar genes determine radically different structures.2. Organisms with different genes produce similar structures.Example: Pax6 in fruit flies, mice and humans

  • Genetics: Homolog structures and genesIs there a correlation between genotype and phenotype?

    Pax6 in fruit flies, mice and humans:"master regulator of eye development (qtd. in Displan,1997). Downstream genes are not the same, thus determines different structures.

  • How would you test common ancestry?Fossil recordStructure and positionbehavioral patternsGenetics Developmental pathways

  • Wells Critique: Developmental PathwaysAssumption: homologous features should develop in similar waysProblems1. Similar pathways may produce very dissimilar features. 2. Similar features are often produced via very different pathways.Haeckels drawingsGilbert, S. F. 1997. http://7e.devbio.com/about.php

  • Developmental pathways: shared features, shared early developmental features ,presence and sequence of development stages.http://www.natcenscied.org/icons/icon4haeckel.html

  • How would you test common ancestry?Fossil recordStructure and positionbehavioral patternsGenetics Developmental pathways

    others?

  • AnalogyDifferent structures which perform the same function (Owen, 1843)Convergence: Similarities between organisms that evolved independently. Tasmanian wolfMexican wolf

    **How to explain similarities bt organisms? how are related these organisms according to their similitude ? How did they acquire these characteristics?Some terminology was applied in an attempt to define these observed patterns**Owens criterion to define homology is restricted to the phenotype. Its based in the concept of archetype o ideal organism.In Darwins definition there is an ideal organism but the homologies observed imply descendent with modification.

    *One counterargument to Darwins definition is that homology is defined by a circular reasoning. A feature is tested across many groups, looking for patterns and many features can be tested simultaneously against genealogy. The result of multiple tests become more severe than the result of it component tests. Many hypothesis can be evaluated independently and

    ****pax6 can lead the formation of simple and compound eyes, in a broad range of species, it sequence its highly conserved***Analogy defined from an anatomical perspective.Evolutionary definition