ap bio unit 7

• mechanism of natural selection: because resources are limited in nature, organisms with HERITABLE traits that favor survival and reproduction will tend to leave more offspring than their peers, causing the traits to increase in frequency over generations

  • natural selection causes populations to become adapted
• darwin's concept of natural selection observations:

  • traits are often heritable
  • more offspring are produced than can survive (creates competition for limited resources)
  • offspring vary in their heritable traits
• natural selection doesn't sense what the population "needs"

  • instead, adaptations occur due to more offspring and mutations occur due to random chance
• we DONT ACQUIRE traits
• 6 mechanisms of evolution (hand):

  • small population
  • non-random mating
  • mutation
  • gene flow (immigration, emigration)
  • genetic drift
  • natural selection
• artificial selection: when humans purposefully breed organisms with desirable traits in order to increase the frequency of those traits in the population
• genetic drift: may result in the loss of some alleles and the fixation of others

  • bottleneck effect- when the size of a population is reduced due to natural disasters
  • founder effect- when a small group breaks off from a larger population to establish a colony (isolated)
  • founder effect occurs via colonization

  
• microevolution = change in allele frequencies over time
• natural selection and evolution act on an organism's PHENOTYPE
• stabilizing selection: favors the intermediate phenotype

  
• directional selection: favors one extreme phenotype

  
• disruptive selection: favors both extreme phenotypes

  
• gene flow: transfer of genetic material between populations
• hardy-weinberg equilibrium: NO EVOLUTION IS OCCURRING
• evidence for macroevolution:

  • anatomy and embryology
  • molecular biology
  • biogeography
  • fossils
• biogeography: study of geographical distribution of organisms
• homologous vs analogous features:

  • physical features due to a common ancestor are homologous (same structure, different function) (ex. human arm and bird wing)
  • physical similarities NOT due to a common ancestor are analogous (organisms live in similar environments or experience similar selective pressures)
• divergent evolution = homologous structures (same species move AWAY)

  convergent evolution = analogous structures (two distantly related species COME together)
• evidence for evolution molecular biology:

  • same genetic material
  • same genetic code
  • same basic process of gene expression
  • biologists often compare homologous genes
• phylogenetic tree: hypotheses, NOT definitive facts

  • constructed based on physical traits and the DNA sequences of their genes
  • organize species into nested groups based on shared derived traits (traits different from those of the group's ancestor)
• allopatric speciation: evolve into separate species due to geographical separation

  sympatric speciation: evolve into separate species WITHOUT geographical separation
• prezygotic barriers:

  • Geographic isolation
  • temporal isolation (mate at different times of the day/year)
  • behavioral isolation (courtship behaviors)
  • gametic isolation (can't fertilize)
  • mechanical isolation (bodies or reproductive structures that don't fit together)
• adaptive radiation: period of evolutionary change in which new species form as populations adapt to different ecological niches
• species: group of organisms that can interbreed and produce viable offspring
• postzygotic barriers:

  • reduced hybrid viability (hybrid has impaired development)
  • reduced hybrid fertility (hybrid can develop into a healthy adult, but is sterile)
  • hybrid breakdown (hybrid of the first generation may be fertile, but when they mate, their offspring will be sterile)
• highly inbred population = low genetic diversity
• • earth formed around 4.5 billion years ago
  • earth was capable of supporting sustained life about 3.9 billion years ago
  • earliest fossil evidence dates back to 3.5 billion years ago
• miller urey experiment:

  • used water, ammonia (NH3), methane (CH4), and hydrogen (H2)
  • to simulate the lightning that provided energy for chemical reactions in Earth's early atmosphere, they sent sparks of electricity through the experimental system
  • found that various types of amino acids and other organic molecules had formed
  • NO OXYGEN PRESENT
  • NO DNA FORMED

  
• RNA world hypothesis: RNA was the first self-replicating genetic molecule on earth

  • proof: ribozymes are RNA molecules that catalyze chemical reactions
• in hardy-weinberg equilibrium, the degree of freedom is ALWAYS 1 (because there are only two alleles)
• Sympatric speciation: new species from surviving ancestral species while both continue to inhabit the same geographical region

  • habitat isolation
  • behavioral isolation
  • sexual selection
  • polyploidy