GENERAL BIOLOGY

• 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.