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Biology LibreTexts

2.1: Taxonomy and Phylogeny

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  • Taxonomy vs. phylogeny?

    • Taxonomy is the science/study of classification.
    • Phylogeny is the science/study of evolutionary relationships between organisms.

    Modern taxonomy is based on phylogeny.

    • Nucleic acid sequencing (of DNA and/or RNA) is used to establish evolutionary relationships between organisms.
    • Taxonomic levels for cellular organisms from most inclusive to least inclusive:

    Domain, Kingdom, Phylum, Class, Order, Family, Genus, specific epithet (genus + specific epithet= unique species name)

    Binomial nomenclature and naming cellular organisms

    • cellular=made of cells
    • All cellular organisms have a “scientific name”
    • the scientific name consists of a genus name (Capitalized) and a specific epithet (lower case)
      • together this 2-part name is the “speciesname.
      • This system of naming was developed by Carolus Linnaeus and is called the “binomial nomenclature” (“two term name”)
    Common name Scientific name
    humans Homo sapiens
    bacterium in gut Escherichia coli

    -Note in the examples, Homo and Escherichia are the genus names, sapiens and coli are the specific epithets. Also note the convention of making the scientific name/species name appear different from surrounding text; this is usually accomplished by using italics or underlining. Also note that the genus name can be abbreviated by using the first letter only.

    • Homo sapiens =H. sapiens
    • Escherichia coli = E. coli

    Sizes of microbial pathogens

    “microbial” =so small, requires microscope to visualize. metric units used in microbiology:

    • mm=millimeter=10-3 meter (one thousandth meter)
    • µm = micrometer 10-6 meter (one millionth meter)
    • nm=nanometer=10-9 meter (one trillionth meter)

    resolution limit of human eye ~ 100 micrometers µm = ~ 0.1 mm

    • bacteria ~ 1µm (µm = 10-6 meter)
    • viruses 30-300 nm (nm=10-9 meter )
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