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