Phylogenetic Classification (AQA AS Biology): Revision Note

Phylogenetic classification

• Phylogenetics is the study of how organisms are evolutionarily related — often shown using a phylogenetic tree

• The phylogenetic system of taxonomy arranges organisms into groups based on their evolutionary origins and relationships

• Under the phylogenetic classification system:

  • there is a hierarchy of groups, in which smaller groups are placed within larger groups

  • there is no overlap between groups

  • each group is called a taxon (plural taxa)

• Phylogenetic systems use DNA, RNA, and protein similarities to identify evolutionary links

  • For example, two species with more similar DNA sequences are assumed to have a more recent common ancestor

• Grouping organisms in this way is helpful for several reasons

  • Scientists can communicate clearly about different species

  • Knowledge that relates to one species can often be partially applied to other, closely related species, e.g. if one species in a taxon has medicinal properties then it is likely that other species will too

  • It allows scientists to gain an accurate count of the number of species, which is useful for conservation purposes

• Biological classification changes as more molecular analysis is completed; this means that phylogenetic classification is becoming more accurate over time

  • E.g. the five kingdoms classification system (animals, plants, fungi, protists, bacteria) has now been incorporated into the three domains system (below)