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Lecture 17

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Western University
Biology 1001A
Tom Haffie

Chapter 19.1-19.6 (Lecture 17) 19.2- Systematic Biology: An Overview • Convergent evolution refers more to distantly related organisms and parallel evolution to more closely related ones. The evolution of flight is convergent between insects (phylum Arthropoda) and vertebrates (phylum Chordata, birds, pterosaurs, and bats) and parallel within the vertebrates • The Science of Systematics has two major goals o Goal 1: To reconstruct the phylogeny or evolutionary history of a group of organisms.  Presented as phylogenetic trees; formal hypotheses identifying likely relationships among species  Allow us to distinguish similarities inherited from a common ancestor from those that evolved independently in response to similar environments o Goal 2: Taxonomy; the identification and naming of species and their placement in a classification  A classification is an arrangement of organisms into hierarchical groups that reflect their relatedness  In the Linnaean system, a family is a group of genera that closely resemble one another. (DomainKingdomPhylumClassOrderFamilyGenusSpecies) • Organisms are classified based on features such as morphological traits; chromosomal anatomy; gene sequences; details of physiological functioning; morphology of subcellular structures, cells and organ systems; and patterns of behaviour 19.5- Evaluating Systematic Characters • In preparing a phylogeny, systematists seek: o Traits in which phenotypic variation reflects genetic differences rather than environmental variation o Genetically independent traits, which reflect different parts of an organism’s genome • Homologous traits- Characteristics that are similar in two species because they inherited the genetic basis of the trait from their common ancestor (Support true phylogeny) o Phenotypic similarities between organisms reflect underlying genetic similarities o Homologous characters can differ considerably among species • Analogous characters- (homoplasious) phenotypically similar and have similar functions but evolved independently in different lineages o Convergence-misleading similarities; inhabit similar environment; similar body shape o Divergence-misleading dissimilarities; closely related but don’t look alike • Systematists o compare homologous cha
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