4.5.2 Phylogenetic Classification

Key Features of Classification

1. Hierarchical System

• Organisms are grouped into successive levels of increasing specificity:
• Kingdom
• Phylum
• Class
• Order
• Family
• Genus
• Species

2. The Five Kingdoms

• Animalia (animals)
• Plantae (plants)
• Fungi (e.g., mushrooms, moulds)
• Prokaryotae (bacteria)
• Protoctista (unicellular organisms like amoeba)

3. Binomial Naming System

• Organisms are given a two-part Latin name:
• Genus (capitalised)
• Species (lowercase)
• Example: Homo sapiens (humans).

Phylogenetic Classification

Phylogenetics is the study of evolutionary relationships between organisms. This system uses common ancestors and shared characteristics to group organisms.

• Molecular Phylogeny
  • DNA, RNA, and protein sequences are compared to assess the genetic similarities and differences between organisms.
  • The more similar the sequences, the more closely related the organisms.
• Phylogenetic Trees
  • Show the evolutionary relationships between species.
  • Branch points represent common ancestors, and the closer two species are on the tree, the more closely related they are.

The Three Domains

Recent advances in molecular phylogeny have led to the reclassification of organisms into three domains based on genetic data:

4. Bacteria

• True bacteria with peptidoglycan in their cell walls.

5. Archaea

• Prokaryotic organisms that live in extreme environments, such as hot springs or salty lakes.

6. Eukaryota

• All eukaryotic organisms, including plants, animals, fungi, and protists.