DL

Unit 9: Evolution and Population Genetics

Evidence of Evolution

  • The Fossil Record
    • Paleontology - The study of fossils
    • Fossils - The remains or traces of an organism that lived in the distant past
      • Remains - Parts of the actual organism, i.e bones, teeth, and shells
      • Traces - Evidence of the organism upon their environment, i.e footprints, trails, and burrows
    • Provides information of certain parts of the past; when all put together, shows a history of when different plants and animals were around
    • Fossil layers are studied using the Law of Superposition
    • The Law of Superposition tells us that the oldest fossils are found at the bottom layer of the Fossil Record.
    • Comparing different layers of the Fossil Record shows the change in organisms alive at certain periods of history.
  • Comparative Anatomy
    • Homologous Structure - Features that are similar in structure but appear in different organisms and are used for different function)
    • Shows the organisms have similar genes and are potentially descended from a common ancestor.
    • Vestigial Structure - Non-functioning remnants of similar organs in other species
    • Shows the evolutionary past of an organism
    • Shows the organism may have a common ancestor with other species that have a similar structure
    • Examples: Human tailbone & appendix, whale pelvis
    • Embryology - The study of embryos
    • Embryos of different species that appear similar in early stages of development may indicate a common ancestor
  • Bio-Chemical
    • All living this are based on a universal genetic code(DNA)
    • Triplets of DNA nitrogen-base sequences(codons) almost always code for the same amino acid regardless of the organism they are in
    • Similar DNA implies that the organisms are similar; The more genes they share, the more similar the organisms are
      • A cladogram displays this data and is used to show the evolutionary relationship between different organisms
  • Observable Events
    • Some changes in species have been observed and studied
    • Peter & Rosemary Grant’s study of beak size in Darwin’s finches
    • H. Kettlewell’s Study of Peppered Moths
    • Evolution of Antibiotic Resistance in bacteria like MRSA
    • Flu Virus
    • Shows evolution is an ongoing process
  • Bio-geography
    • \

Charles Darwin

  • Definitions:
    • Species: A group of organisms that can interbreed and have fertile offspring
    • Population: A group of the same species living together in the same area
    • Adaptation: Any mutation(genetic) that helps an organism survive in its environment
    • Extinction: The elimination of every single member of a species
    • When an entire species fails to adapt to a changing environment, they are likely to go extinct
  • Background:
    • Born in Shrewsbury, England (1809)
    • Study medicine at Edinburgh
    • Repulsed by blood / surgery
    • Studied to become a Clergyman at Cambridge University
    • Went on survey trip on the HMS Beagle
    • Lasted 5 years
    • Worked as a naturalist
    • Made many observations and collected evidence for his theory of how life changes
  • Context:
    • People during the time period he was alive believed that Earth doesn’t change/evolve and in the idea of “fixity of species“
    • *fixity of species: species never change
    • Darwin began to disagree after studying a bunch of animals
  • Evidence:
    • Darwin related the finches in the Galapagos Islands with those he had seen in South America, and realized they must have migrated from South America to the Galapagos Islands.
    • Once there, they must’ve evolved over time into what they look like today.
  • Conclusion
    • Darwin concluded that each species descended with changes from other species over time. Darwin called this “descent with modification“, or evolution.
    • Extending evolution to biology, Darwin developed his idea of “natural selection“
    • He proposed that natural selection was the way in which evolution occurred
    • He published his findings and theories in a book called “On the Origin of Species“
    • 5 Components of Natural Selection
    • All Species have genetic variation
      • Caused by mutation and gene shuffling
    • Organisms produce more offspring than can survive
      • Many that survive don’t reproduce
    • Since more organisms are produced than can survive, there is competition
      • The struggle for survival is affected by both short and long term environmental changes
      • Compete for resources and a mate
    • Survival of the fittest
      • Organisms that are better adapted to their environment are more likely to survive, and pass down their traits to offspring.
      • Over time, this ensures that helpful mutations such as fur colors that help camouflage are passed down to offspring and become common in a certain species
    • Descent with modification

Genetic Equilibrium

  • Evolution can be defined as the change in the frequencies of alleles in the gene pool of a population over a period of time.
  • Evolution is caused when genetic equilibrium is disrupted
    • Genetic equilibrium can be depicted as a bell curve graph
    • *Allele frequency stays constant
  • Reasons that Stability is Disrupted
    • Natural Selection
    • “Survival of the Fittest“ (Darwin’s Theory)
    • Only force that directly increases the fitness of a population
    • Can shift phenotype distribution in 3 ways
      • Stabilizing Selection
      • Eliminates extremes
      • Reduces genetic variation
      • Directional Selection
      • Against the average alleles
      • Favors extremes
      • Disruptive Selection
      • Moves the average (entire graph) in one direction
    • Migration
    • Causes a change in Gene Flow
      • Gene Flow: The movement of alleles from one population to another, which changes the allele frequencies in each population
    • Immigration (moving in) increases diversity
    • Emigration (moving out) decreases diversity
    • Isolation
    • Prevents parts of a population from mating with each other, reducing the gene pool for each part of the fractured population.
    • An example of divergent evolution
    • Leads to speciation
    • Mutation
    • Provides the only source of new alleles in a species
    • Genetic Drift
    • A chance occurrence that dramatically changes allele frequencies
    • Typically kills off a huge chunk of the gene pool
    • Usually a natural disaster, i.e Tsunamis, hurricanes, etc
    • Sexual Selection
    • Certain traits that improve mating success i.e feather/fur color increase in frequency due to a higher chance of reproduction
  • Hardy-Weinberg Equilibrium
    • If the following conditions are met, the population’s alleles and genotype frequency will not change and thus evolution will not occur
    • Large population
    • No mutations of the alleles
    • No migration
    • No sexual selection
    • No natural selection
  • Pocket Mouse Video
    • Variation
    • Mutation in the gene Mc1r caused the mouse to turn black
    • Over Reproduction
    • Struggle for Existence
    • Constantly getting eaten by hawks, snakes, etc
    • Some are more fit
    • Color of the pocket mice
      • The normal fur color of the pocket mouse lets them blend in well with the sand, but on the new cooled-lava terrain, they stand out
      • The evolved dark colored mice are better able to hide in the new terrain, and thus are better at surviving
    • Descent with Modification