Chapter 20 2/3

Evolution and Classification of Organisms

Evolutionary Change Over Time

  • Populations can shift over generations, influenced by traits being passed down.

  • Horizontal gene transfer is significant in comparing different bacterial populations.

Phylogeny

  • Definition: Phylogeny refers to the evolutionary history of a species or group.

  • Phylogenetic traits are used to classify organisms and explore their evolutionary relationships.

  • Systematics is the discipline that classifies organisms based on their phylogenic relationships.

Taxonomy

  • Taxonomy: Order, division, and naming of organisms based on resemblance and genetic makeup.

  • Originally defined by Carolus Linnaeus in the 18th century, based on physical appearances.

  • Modern taxonomy incorporates DNA sequencing to classify organisms.

  • Binomial nomenclature: Two-part naming system introduced by Linnaeus.

    • Example: Humans are classified as Homo sapiens (genus and species).

    • The first part (genus) is capitalized, while the second part (species) is lowercase and italicized.

Taxonomic Hierarchy

  • Classification ranges from broad domains to narrow species:

    • Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species.

    • Mnemonic: "Did King Philip Come Over For Great Spain?"

Levels of Taxonomy

  • Domain: The broadest category, e.g., Eukarya (eukaryotic organisms).

  • Kingdom: Includes multicellular, heterotrophic organisms like animals.

  • Phylum: Chordates, organisms with a notochord.

  • Class: Mammals, characterized by mammary glands.

  • Order: Carnivora, includes carnivorous animals.

  • Family: For example, Felidae (cat family) and Canidae (dog family).

Understanding Relationships

  • Sister taxa: Groups of organisms sharing an immediate common ancestor.

  • Taxa are units at any level of the hierarchy; closely related species share more recent common ancestors.

Phylogenetic Trees

  • Graphical representations of evolutionary relationships among species.

  • Branch points represent common ancestors where species diverged.

  • Rooted trees display ancestral lineage with the oldest common ancestor at the base.

  • Examples of divergence:

    • From water to land: Fish diverged early, while frogs adapted to both.

    • Chimpanzees and humans are considered sister taxa, sharing a common ancestor.

Divergence Types

  • Basal taxon: Diverges early in the history of a lineage.

  • Polytomy: A branch point from which more than two groups emerge, indicating an unresolved pattern of divergence.

Key Points to Remember for Examination

  • Ability to identify organisms classified under specific taxa (genus, family, etc.).

  • Recognition of sister taxa when comparing evolutionary trees.

  • Understand phylogenetic tree structures, including common ancestors and divergent points.