17.2 Modern Classification

17.2 Modern Classification

• 1.
  Typological Species Concept 17.2Modern Classification Organizing Life’s Diversity  Aristotle and Linnaeus thought of each species as a distinctly different group of organisms based on physical similarities.  Based on the idea that species are unchanging, distinct, and natural types. Chapter 17
• 2.
  Biological Species Concept OrganizingLife’s Diversity  The biological species concept defines a species as a group of organisms that is able to interbreed and produce fertile offspring in a natural setting. 17.2 Modern Classification Chapter 17
• 3.
  Phylogenic Species Concept OrganizingLife’s Diversity  Phylogeny is the evolutionary history of a species.  The phylogenic species concept defines a species as a cluster of organisms that is distinct from other clusters and shows evidence of a pattern of ancestry and descent. 17.2 Modern Classification Chapter 17
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  Organizing Life’s Diversity 17.2Modern Classification Chapter 17
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  Characters  To classifya species, scientists construct patterns of descent by using characters. Organizing Life’s Diversity  Characters can be morphological or biochemical. 17.2 Modern Classification Chapter 17
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  Morphological Characters  Sharedmorphological characters suggest that species are related closely and evolved from a recent common ancestor. Organizing Life’s Diversity  Analogous characters are those that have the same function but different underlying construction.  Homologous characters might perform different functions, but show an anatomical similarity inherited from a common ancestor. 17.2 Modern Classification Chapter 17
• 7.
  Birds and Dinosaurs OrganizingLife’s Diversity  Compare birds and dinosaurs:  Hollow bones  Theropods have leg, wrist, hip, and shoulder structures similar to birds.  Some theropods may have had feathers. Haliaeetus leucocephalus Oviraptor philoceratops 17.2 Modern Classification Chapter 17
• 8.
  Biochemical Characters Organizing Life’sDiversity  Scientists use biochemical characters, such as amino acids and nucleotides, to help them determine evolutionary relationships among species.  DNA and RNA analyses are powerful tools for reconstructing phylogenies. 17.2 Modern Classification Chapter 17
• 9.
  Organizing Life’s Diversity The similar appearance of chromosomes amongchimpanzees, gorillas, and orangutans suggests a shared ancestry. 17.2 Modern Classification Chapter 17
• 10.
  Molecular Clocks Organizing Life’sDiversity  Scientists use molecular clocks to compare the DNA sequences or amino acid sequences of genes that are shared by different species. 17.2 Modern Classification Chapter 17
• 11.
  Organizing Life’s Diversity The differences between the genes indicate the presence of mutations.  The more mutations that have accumulated, the more time that has passed since divergence. 17.2 Modern Classification Chapter 17
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  The Rate ofMutation is Affected Organizing Life’s Diversity 17.2 Modern Classification  Type of mutation  Where the mutation is in the genome  Type of protein that the mutation affects  Population in which the mutation occurs Chapter 17
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  Phylogenetic Reconstruction Organizing Life’sDiversity  Cladistics reconstructs phylogenies based on shared characters.  Scientists consider two main types of characters when doing cladistic analysis.  An ancestral character is found within the entire line of descent of a group of organisms.  Derived characters are present members of one group of the line but not in the common ancestor. 17.2 Modern Classification Chapter 17
• 14.
  Cladograms Organizing Life’s Diversity The greater the number of derived characters shared by groups, the more recently the groups share a common ancestor. 17.2 Modern Classification Chapter 17