Phylogeny

• Phylogeny


  • describes relationships of organism as which organism it is thought to have evolved from;
  • which species it is most closely related to
• Phylogenetic Tree


  • also known as Tree of Life
  • a tool used to study phylogeny
  • is a diagram that represents evolutionary relationships among organisms. These are hypotheses, not definitive facts. The pattern of branching in a phylogenetic tree reflects how species or other groups evolved from a series of common ancestors
• Phylogeny


  Identify the characters, that vary among species. These can be:

  1. Morphological/anatomical features
  2. Physiological Adaptations
  3. Molecular sequences
  4. Behavioral or ecological
• The more same characteristics/features, the more related the organisms are. But looking and only focusing on that can be MISLEADING... and can lead to what we called HOMOPLASY. To prevent that mistake and misleading we have the CLADISTICS.
• Homoplasy


  • shared characters that are not a result of common ancestry, but of independent evolution of similar characters.
  • can result from convergent evolution
• Cladistics


  a way of classifying organisms into hierarchical branches based on shared derived characteristics.
• Derived Characteristics


  • similarity that is inherited from the most recent common ancestor
  • presence of hair in mammals
• Ancestral Characteristics


  • similarity that arose prior to the common ancestor of the group
  • presence of backbone in all mammals and other vertebrates
• Symplesiomorphy


  shared ancestral characters
• Synapomorphy


  a derived character that is shared by all the members of the clade
• Outgroup


  not part of the group of interest (the ingroup) but also not too distantly related to it.
• The outgroup is used to polarize the character states, or infer change. The character state possessed by the outgroup is defined a priori as ancestral (pleisiomorphic).
• Cladistics


  a way of classifying organisms into hierarchical branches based on shared characteristics.
• Cladogram


  is a branching tree diagram that shows ancestral relationships among organisms
• Clade


  a group of organisms believed to have evolved from a common ancestor, according to the principles of cladistics.
• Root

  is the initial common ancestors of all the organisms in a cladogram
• A root is the starting point for any given cladogram. However, the root might also indicate that it comes from some other larger clades.
• Nodes


  Each of this is a hypothetical ancestor that gives rise to two or more daughter taxa.
• Nodes


  indicate the bifurcating (divide in to two) branch point of divergence in all cladograms
• Nodes


  exists in each point where a group of organisms divides or separate into further different groups
• Taxon


  Also called outgroup is the most distantly related group of animals that isn’t necessarily a clade
• Taxon


  This functions as a point of reference or comparison for the rest of the cladogram.
• Branches


  is a line that connects all the other parts of the cladogram
• The branch length in some cases represents the extent of divergence or the extent of the relationship among different taxa.
• Sister Groups


  is a pair of taxa that are most closely related to each other.
• Monophyletic


  consists of the ancestor species and all its descendants.
• Paraphyletic


  consists of an ancestral species and some, but not all of the descendants
• Polyphyletic


  includes many species that lack a common ancestor.
• The Principle of Parsimony


  The less evolutionary steps are better than more steps to explain relationships. The tree with the least number of steps is the most parsimonious.
• Various Tree Layouts

  1. Rooted Phylogenetic tree
  2. Unrooted phylogenetic tree