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Biology LibreTexts

2.1: Taxonomy and Phylogeny

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 )