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General Biology: Phylogeny & Tree of Life

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  • Taxon

    any named group of organisms used in classification.

  • Binomial Nomenclature

    A system of naming species using two names: Genus (capitalized) and species epithet (lowercase), e.g., Puma concolor.
  • Homology

    Homology is similarity of parts or organs in different animals due to common ancestry.
  • Homoplasy

    Homoplasy is similarity due to convergent evolution, not common ancestry.
  • Monophyletic Group

    A group consisting of an ancestor and all of its descendants; also called a clade.
  • Paraphyletic Group

    A group consisting of an ancestor and some, but not all, of its descendants.
  • Polyphyletic Group

    A group consisting of distantly related organisms but does not include their most recent common ancestor.
  • Synapomorphy

    A shared derived character present in two or more taxa indicating common ancestry.
  • Autapomorphy

    A unique derived character found only in a single taxon.
  • Sister Taxa

    Two taxa that are each other's closest relatives, sharing a most recent common ancestor.
  • Cladogram

    A branching diagram showing ancestor-descendant relationships based on common ancestry.
  • Phylogenetic Systematics (Cladistics)

    Classification of organisms based on common ancestry, grouping taxa by shared derived characters.
  • Fossil Record

    Preserved evidence of past life in sedimentary rocks, used to study evolutionary history.
  • Relative Age Dating

    Determining fossil age by position in rock layers; older fossils are found below younger ones.
  • Absolute Age Dating

    Using radiometric methods to determine the exact age of fossils based on isotope decay rates.
  • Half-life

    The time required for 50% of a radioactive isotope to decay, e.g., C14 has a half-life of 5730 years.
  • Maximum Parsimony

    The simplest phylogenetic tree with the fewest evolutionary changes is preferred.
  • Linnaean Taxonomy

    An early system grouping organisms by overall similarity without considering evolutionary relationships.
  • Problems with Linnaean Taxonomy

    Ranks are arbitrary and may not reflect evolutionary history; e.g., birds classified inside reptiles.
  • Evidence for Common Ancestry

    Includes comparative anatomy, genetics, fossil record, and shared derived characters.