Unit 7

• Natural selection


  Mechanism of evolution, how species adapt in environment over time with variations and traits
• How does natural selection lead to evolution?


  The more the organism adapted to environment, the more likely to survive and reproduce
• Darwin's theory of natural selection

  Characteristics inherited, more offspring must be produced than can survive, fittest offspring survive and reproduce
• Differential survival


  Differences between rates of survival of some individuals in a group, population or species
• Organisms require competition for limited resources to allow for natural selection
• Evolutionary fitness


  Success in passing genes to next generation
• Reproductive success


  Likelihood of individual contributing fertile offspring to next generation
• Reproductive success


  Leads to natural selection as desired traits that allowed an individual to survive would be passed on
• Abiotic environment


  Affects direction of evolution through competition for food
• Biotic environment


  Affects rate of evolution through predation and competition for resources
• Abiotic environment


  Climate change makes population evolve much faster, favouring organisms that easily adapt to change
• Phenotype


  Physical traits
• Natural selection acts on phenotype but modifies genotype
• Microevolution


  Evolution on a small scale with fitness increasing alleles becoming more common in population
• Selective pressures


  Interaction between natural variation in species and factors in environment = certain form to have advantage over others
• How does environment apply selective pressure to a population?

  Populations change because individuals with beneficial characteristics survive and reproduce, increasing frequency of that characteristic
• Phenotypic variation that increases fitness


  • Antibiotic resistance in bacteria
  • Rock pocket mouse with lighter fur color living in sandy desert
• Phenotypic variation that decreases fitness

  • Sickle cell mutation in someone living in area without mosquitos carrying malaria
  • Rock pocket mouse with lighter color fur living on dark lava rock
• Abiotic environment


  Affects direction of evolution through organisms' ability to withstand climate change
• Artificial selection


  Identification by humans of desirable traits in plants and animals and steps taken to enhance and perpetuate those traits in future generations
• How does artificial selection modify variation in species?

  Organisms with traits humans value get chosen for breeding next generation, over time the characteristics become more common in a population
• Artificial selection due to humans


  • Dogs
  • Agriculture (wild mustard = ancestor for broccoli, kale, cauliflower)
• Convergent evolution


  Distantly related species resemble one another
• Convergent evolution


  • Sugar glider and flying squirrel
  • Bat and bird wings
• Selective pressures


  Result in similar phenotypic adaptations in similar environments, as organisms better suited for their environment
• Mutations


  Changes to DNA sequence
• Mutations that affect phenotype

  • Point mutation
  • Chromosomal mutation
• Mutations


  Can introduce new alleles/genes into population, leading to new phenotypes
• Genetic drift


  Unpredictable fluctuation of alleles from one generation to the next in small population sizes
• Founder effect


  Certain genotypes of individuals brought to population become over/under represented
• Bottleneck


  Severe drop in population size causes certain alleles to be over/under represented in population
• Gene flow


  Population gaining/losing alleles due to migration
• Gene flow


  Brings new variations of genetic makeups into a population from another population
• Hardy-Weinberg equilibrium


  Describes a population not evolving, with genetic variation and allele/genotype frequencies remaining constant over generations
• Genetic variation is important for a population's survivability, as it enables individuals to adapt to environment and maintain survival
• A decrease in genetic variation affects a population by decreasing its chance of survival due to lack of variation and adaptation ability</b>
• Allele frequency


  Frequencies of dominant and recessive alleles in a population
• Genotypic frequency


  Frequencies of homozygous dominant, heterozygous, and homozygous recessive genotypes in a population
• Biogeography


  The geographic distribution of organisms
• Geographical data


  Supports evolution, as species in nearby areas resemble each other (e.g. Galapagos finches)