cladograms and applying cladistics

• Cladograms


  Used to compare traits (either morphological or molecular) and explore evolutionary links
• Creating a cladogram

  1. Gather traits into a matrix

  2. Use matrix to create cladogram

  3. Cladogram visualises relationships
• Traits used in cladograms

  • Number of limbs
  • Skin covering
  • Reproductive characteristics
• Relationships in cladograms


  Based on the most probable evolutionary relationships ie. the one with the fewest number of sequence changes or development of new characteristics
• Parsimony


  Things are usually connected or behave in the simplest or most economical way
• Cladograms


  • Visual representations of evolutionary relationships
  • Common ancestors
  • Grouping of related organisms into clades
• Root


  Represents the most common ancestor
• Node


  Represents a hypothetical common ancestor
• Terminal branch


  Represents an extant species
• Branching


  Represents the evolutionary relationship between species
• If extinct species are included, information about be given on whether this relationship is purely based on morphology (DNA is usually not available)
• More nodes the more distant the relationship
• Mutations are assumed to occur at a constant rate eg on base change per 10^9 years
• Some cladograms are drawn to scale
• Cladograms can be used to estimate when species diverged and when the common ancestor existed