C9

• PHYLOGENTIC TREES

  • Demonstrates the evolutionary relationship between organisms 
  • Constructed using homologous features -> morphological and molecular 
  • Presents hypothesis of evolutionary relationships 
  • Hypothesis
  • Length of arm = time
  • Node = where time meet
• structural morphology: comparing structures between individuals such as homologous and vestigial structures (this is often done through the fossil record)
• HOMOLOGOUS STRUCTURE

  • Same structure in different organisms but structures serve different functions.

  
• NATURAL SELECTION EXPLAINS HOMOLOGOUS STRUCTURE

  • Species have a recent common ancestor 
  • Subjected to different selection pressures in their environment 
  • Certain traits/phenotypes have a selective advantage and allow certain individuals with advantageous trait to survive and reproduce more 
  • Alleles are passed to offspring where the species have evolved parts that have similar structure but different biological function 
•  

  VESTIGAL STRUCTURES

  • Reduced structures with no apparent function 
• NATURAL SELECTION EXPLAINS VESTIGAL STRUCTURE

  • Variation in the species with a common ancestor 
  • Environmental change causes different selection pressures  
  • Certain traits/phenotypes have a selective advantage and allow certain individuals with advantageous trait to survive and reproduce more 
  • Some structures have no biological advantage or disadvantage to their environment 
  • Alleles are passed to offspring where structures serve no biological purpose to the organism 
•  molecular homology: comparing DNA and amino acid sequences
• 1. Homologues features

  • Similar because the organisms share a common ancestor.
  • Retained through divergent evolution
• 1. Analogous features

  • Similar structure and function but evolved independently
  • Do not share a recent common ancestor
  • A result of convergent evolution.
• COMPARING DNA SEQUENCES

  1. Species with less difference in DNA/amino acid sequence-> more closely related 

  • Diverged most recently from a common ancestor (less accumulation of mutations) 

   2. Species with more difference in DNA/amino acid sequence -> less closely related 

  • Diverged most distantly from a common ancestor (more accumulation of mutation) 
  • More mutations -> more genetically diverged -> more time to accumulate mutations in divergence period + recent divergence from common ancestor -> more conserve DNA sequences.
• Why should you compare DNA and not amino acids? 

  • The genetic code is degenerate where an amino acid is coded for by more than one codon 
  • DNA sequences are much more specific, holding three nucleotides for each amino acid, this allows more possible mutations to be identified 
• Conservation = amnio acids

  Mutations = mutations
• Type of molecular feature 

  Criteria  

  Analogous  

  • Same function 
  • Homologous 
  • Same function 
  • Same ancestor 
  • Same structure 
• VESTIGAL STRUCTURES

  • Reduced structures with no apparent function 
• NATURAL SELECTION EXPLAINS VESTIGAL STRUCTURE

  • Variation in the species with a common ancestor 
  • Environmental change causes different selection pressures  
  • Certain traits/phenotypes have a selective advantage and allow certain individuals with advantageous trait to survive and reproduce more 
  • Some structures have no biological advantage or disadvantage to their environment 
  • Alleles are passed to offspring where structures serve no biological purpose to the organism 
• Homologous structures share an ancestor but serve a different function but analogous structures serve a similar function but do not share an ancestor. Vestigial structures are traits that our ancestors needed but no longer serve a purpose in our environment.