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