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Chapter 14 Section 2

Chapter 14 Section 2. How Biologists Classify Organisms. Grade 10 Biology Spring 2011. What is a Species?. Biological species: a group of natural populations that are interbreeding or that could interbreed, and that are reproductively isolated from other such groups. What is a Species?.

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Chapter 14 Section 2

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  1. Chapter 14 Section 2 How Biologists Classify Organisms Grade 10 Biology Spring 2011

  2. What is a Species? • Biological species: a group of natural populations that are interbreeding or that could interbreed, and that are reproductively isolated from other such groups

  3. What is a Species? • Hybrids: sometimes individuals of different species interbreed and produce offspring • Species are closely related when they can interbreed and produce fertile hybrids

  4. Evaluating the Biological Species Concept • Works well for most members of kingdom Animalia • Some species are able to form fertile offspring with closely related species • Fails to describe species that reproduce asexually • Biologist recognize species by studying an organism’s features

  5. Evolutionary History • Classification based on similarities should reflect an organism’s phylogeny • Its evolutionary history • This can be misleading, not all characters are inherited from a common ancestor • Wings of bird vs. wings of insect

  6. Evolutionary History • Convergent evolution: similarities evolve in organisms not closely related to one another, often because the organisms live in similar habitats • Analogous structures: similarities that arise through convergent evolution

  7. Evolutionary History • Divergent evolution: similarities evolve in organisms not closely related to one another

  8. Cladistics • Cladistics: method of analysis that reconstructs phylogenies by inferring relationships based on shared characters • Can be used to hypothesize the sequence in which different groups of organisms evolved

  9. Cladistics • Ancestral character: with respect to two different groups, a character is defined as an ancestral character if it evolved in a common ancestor of both groups • Ex. Birds and mammals, backbone is an ancestral character

  10. Cladistics • Derived character: evolved in an ancestor of one group but not of the other • Ex. Feathers evolved in an ancestor of birds that was not also ancestral to mammals

  11. Cladistics • Cladogram: branching diagram, shows the evolutionary relationships among groups of organisms

  12. Evolutionary Systematics • Evolutionary systematics: taxonomists give varying degrees of importance to characters and thus produce a subjective analysis of evolutionary relationships • Phylogenetic tree: branching diagram based on evolutionary systematics

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