GENERAL BIOLOGY

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  • Taxonomy
    The science of organizing and categorizing living organisms into classes called taxa
  • Systematics
    The study of the diversification of life forms over time, both past and present, and their relationships between other species
  • Both a systematist and a taxonomist provide: scientific names, detailed descriptions of organisms, collect and keep volumes of specimens, offer classifications for the organisms
  • However, it is the systematist that investigates on evolutionary histories and considers environmental adaptation of species
  • Taxonomic classification (Linnaean system)
    • Uses a hierarchical model
    • Moving from the point of origin, the groups become more precise until the branch terminates as a single species
  • Phylogeny
    The study of relationships and their evolutionary development among different groups of organisms
  • The more distant the relationship between two related species, the farther back in time they shared a common ancestor
  • Phylogenetic tree (tree diagram)
    • Basal taxon - lineage that evolved early from the root that remains unbranched
    • Sister taxa - two lineages stemming from the same branch point
    • Polytomy - branch with more than two lineages; it serves to illustrate where scientists have not definitively determined all of the relationships
  • Although sister taxa and polytomy do share an ancestor, it does not mean that the groups of organisms split or evolved from each other
  • Cladistics
    A method of hypothesizing relationships among organisms, established by Willi Hennig in the 1950s
  • Cladogram
    A diagram showing evolutionary relationships within one or more clades
  • Monophyletic group (clade)

    • A collection of organisms that include an ancestor species and all of their descendants
    • Can be separated from the root with a single cut
  • Paraphyletic group

    • Needs two or more cuts to separate from the root
  • Polyphyletic group

    • Needs two or more cuts to separate from the root
  • Grouping 1 in Figure 9 is monophyletic, grouping 2 is paraphyletic, and grouping 3 is polyphyletic
  • DNA molecules are long chains of nucleotides twisted into a double helix shape.