BIOEB201 - Evolution

• Big Bang


  13.7 Bya
• Milky Way


  ~10 Bya
• Earth


  4.6 Bya
• Oceans


  4.5 Bya
• Strong evidence for life, bacteria-like microfossils and stromatolites (microbial reefs created by cyanobacteria)

  3.4-3.5 Bya

  
• Anaerobic (low oxygen)
• Emergence of life


  1. Photosynthesis (3.8 Bya? But great increase in O2 2.4 Bya)

  2. Aerobic respiration

  3. Prokaryotes: archaea and bacteria dominate until ~1.5 Bya

  4. Eukaryotes (~1.8-2 Bya)

  5. Multicellular organisms ~0.5 Bya
• Endosymbiosis


  Origin of eukaryotes
• Endosymbiosis


  • Mitochondria and chloroplasts have their own membranes, inner membrane chemically like that of Eubacteria, outer membrane like other eukaryotic cell membranes
  • Both have their own circular DNA, usually lack introns and histones
  • Their ribosomes resemble those of prokaryotes, not eukaryotes
  • Both replicate by binary fission
• Mitochondria event happened early → all eukaryotes have them
• Multicellularity


  • An oxygen-rich atmosphere provided the conditions to support evolution of multicellular life
  • Aerobic respiration supplies cells' energy needs → releases much more energy per molecule of glucose than anaerobic
  • Has evolved many times from unicellular ancestors
• Benefits of multicellularity


  • Larger size protects from predators (swallowing by unicellular)
  • Division of labour → different cell types, different functions
  • Allowed increase in size and elaborate organ systems
• Animals most closely related to unicellular choanoflagellates
• Cambrian explosion


  • For the first 10 My, animal diversity low
  • Then, within 20 My, almost all modern phyla and classes of skeletonised marine animals appear in the fossil record → the most dramatic adaptive radiation in history
  • Genetic and ecological causes?
• *Tiktaalik - transitional fossil
• Mesozoic


  • Predation escalated → ability to crush and withstand crushing
  • Rise of the angiosperms and co-evolution with insects
  • Amniote vertebrates (reptiles, mammals, birds) became very diverse
• Every new individual is built from inherited instructions
• Changes in instructions possible only in genes
• Only changed genes can produce changed adults
• Noted different (but similar) species on different islands (finches, mockingbirds, tortoises)
• Descent with modification


  • Accumulate differences slowly over time
  • Modification from ancestor, great family tree
  • Changes in proportions of variants within a population (vs an individual)
• Natural selection


  • The chief mechanism/cause of evolutionary change
  • Survival of the fittest → fitter individuals differ only slightly from the population norm, but the advantageous feature gradually evolves to become more different because new advantageous variants continue to survive (and pass their characteristics on)
• Single ancestor; lineages arise by splitting, not necessarily increasing in complexity
• Pangenesis


  Mechanism of Lamarckian inheritance of acquired characters - 'gemmules' control body parts; unite in gonads to pass heritable information to gametes
• Blending inheritance


  Characters inherited as the average of the parents' values
• Law of segregation


  Each inherited trait is defined by a gene pair; parental genes are randomly separated so that sex cells contain only one gene of the pair; offspring therefore inherit one genetic allele from each parent when sex cells unite in fertilisation
• Law of independent assortment


  Genes for different traits are sorted separately so the inheritance of one trait is not dependent on the inheritance of another
• Law of dominance


  An organism with alternate forms of a gene will express the form that is dominant
• Particulate inheritance


  The inheritance of discrete characters via genes that are independently expressed without blending from generation to generation → variation can persist (not decrease)
• The modern synthesis or neo-Darwinism

  Adaptive evolution is caused by natural selection acting on particulate (Mendelian) genetic variation
• Major causes of evolution within species (microevolution)

  • Mutation
  • Gene flow (migration)
  • Natural selection
  • Genetic drift
• Major causes of evolution among species (macroevolution)

  • Mutation
  • Gene flow (migration)
  • Natural selection
  • Genetic drift
• Genome architecture


  The structure and organization of the genome

  
• DNA is a sequence of four repeating nucleotides that provide structural support to chromosomes

  
• Coding DNA


  DNA that encodes proteins

  
• Non-coding DNA


  DNA that does not encode proteins

  
• No correlation between genome size and complexity

  
• No correlation between number of coding genes and complexity

  
• Land plants and animals have lots of non-coding DNA (up to 99%)
• Most animals and plants have lots of 'junk' DNA