Evolution

Evolution

  • ==Microevolution==::change in allele frequencies over time
    • not always visible in a population unless looking into the genetics and biochem aspects - all kinds of alleles for all kinds of traits that your not always gonna see
  • ==Macroevolution==::Descent with modification; speciation
    • Macroevolution has common ancestors - but changes over time, some changes very visible but others may not be

==Phenotypic Variation==::the currency of evolution

For evolution to occur:

  1. phenotypic variation exists

    1. can be a drive for evolution

  2. traits are heritable

    1. needs a heritable basis
    2. cannot be a environmental differentiation
    3. heritable traits can evolve if they give the bearer a reproductive advantage

  3. differential reproductive success

    1. the variation is accompanied in differences in fitness
    2. if all these tigers have the same amount of gametes and phenotypic success and all have offspring then no evolutionary change will occur

Sources of genetic variation:

  1. Random assortment

    1. Random assortment has 2^23 possibilities

  2. Recombination

    1. Recombination during meiosis

  3. Mutations

    1. Mutations occur during DNA replication (forms a basis of where mutations come from)

Evolutions occurs through random processes and selection

Random Processes:

  1. Mutations

    1. Mutations are DNA copied in a weird way

  2. genetic drift::completely random, not in response to selection

    1. not a genetic process but can lead to a change in species
      • Change in allele frequency between generations based solely on random chance
      • in large populations there are many possibilities and changes within the population have a higher probability of occuring
      • Genetic drift especially potent in small populations
      • Rare genetic diversity gets lost during genetic drift bc of its size and not many chances of change and may hurt the population when change needs to occur like in a environmental change and need for diversity is necessary
      • Genetic drift tends to result in less variation bc rare alleles are lost
      • example: Starts with an even mix of red and blue - but through time you see fewer red and end up with only blue - think at first it’s gonna be natural selection and the red ones might can’t survive in the jar but this doesn’t always have to be bc of genetic drift

  3. bottlenecks

    1. Genetic diversity is lost as a result of bottlenecks
    2. Bottlenecks May or may not inhibit population recovery, but it often does correlate with changes in fitness::
      • frequently decrease fitness
      • usually a response to a particular event
      • when the population size shrinks in a bottleneck so does the genetic diversity
      • when you lose genetic diversity there is lost measurable traits - that may affect the fitness of the overall populations and damage their health later on

  4. founder effects

    1. the reduction in genomic variability that occurs when a small group of individuals becomes separated from a larger population
      • small subset of a population goes and finds a new area to live close or far
      • humans are good for studying this bc we move around alot

Selection:

  1. Artificial selection::human decisions drive which individuals breed, and the phenotype of those individuals increases in frequency (intentional or unintentional)

  2. natural selection::environmental conditions allow one phenotype more reproductive opportunity than another, and the favor phenotype increases

    1. stabilizing selection::selection pressure stays the same and the population becomes more similar through time and we see less phenotypic variation (bell shaped curve continues to get skinnier)

    2. directional selection::it changes the phenotype frequency into something different

      1. example is in a plant population the coloration is greening over time over yellow
      2. in directional selection the selection is pointing towards more pigmented coloration not the color green

    3. disruptive selection::pushes the phenotype into two different directions

      1. In disruptive selection progeny are less like the parents but in two different directions

Phylogenetic trees:: display hypothesized relationships between taxa (read the nodes not the tips)

==Speciation==::depends on ecology and geography Speciation Types

allopatric “different country”

  • allopatric:: is most common
  • Allopatric::physical barrier splits population

Peripatric “near country”

  • Peripatric::small group splits off into a different place
  • Peripatric::new environment has new selective pressures that vary

Parapatric “side-by-side country”

  • Parapatric::continuous population
  • Parapatric::ecological differences in habitat lead to assortative mating

Sympatric “same country”

  • Sympatric::rare
  • Sympatric::selective pressures vary even if within the same river/lake
  • Sympatric::only ecological or genetic barriers (dependence on specific microhabitat / polyploidy::extra sets of chromosomes)