AP Biology: Unit 7 - Natural Selection

Introduction to Natural Selection

• Frequency Dependent Selection
  • Negative Frequency Dependent Selection: Favors less common traits.
  • Positive Frequency Dependent Selection: Favors more common traits.
  • Oscillating Selection: Alternates favoring different phenotypes, often with seasonal changes.
• Industrial Melanism: Selection favors darker individuals (e.g., peppered moths due to pollution).
• Heterozygote Advantage: Heterozygotes have increased reproductive success.

Types of Selection

• Directional Selection: Favors one extreme variation.
• Disruptive Selection: Favors both extremes.
• Stabilizing Selection: Favors intermediates over extremes.
• Relative Fitness: Likelihood of reproduction compared to others.
• Natural Selection: Environment favors certain traits, advantageous traits increase survival.
• Adaptation: Development of favorable traits over time.

Mechanisms of Evolution

• Adaptive Radiation: Many species evolve from one ancestral species.
• Genetic Drift: Gene pool changes due to chance.
  • Bottleneck Effect: Dramatic population decrease alters gene pool.
  • Founder's Effect: New population in uninhabited area changes allele proportions.
• Gene Flow: Exchange of genes between populations.
• Mutation: DNA sequence changes.

Artificial Selection

• Artificial Selection: Human-driven selection (e.g., breeding).
• Genetic Engineering: Direct DNA manipulation.
• Selective Breeding: Deliberate breeding for desired traits.
• GMOs: Genetically Modified Organisms.
• Convergent Evolution: Similar traits evolve independently in similar environments.
• Analogous Structures: Similar function and appearance, different evolutionary origins.
• Divergent Evolution: Species with common ancestry evolve differently.

Population Genetics

• Charles Darwin
  • Natural selection involves survival and reproduction based on trait variations.
• Jean Baptiste Lamarck
  • Use and Disuse theory: Traits change due to use in a lifetime, passed down.
• Hardy-Weinberg Theorem: No effect on gene pool from allele shuffling in meiosis.
  • Equilibrium Conditions: No genetic drift, gene flow, mutations, random mating, or natural selection.
  • Equations:
    • p + 2pq + q² = 1
    • p + q = 1

Macroevolution

• Evolution above the species level, involving large-scale changes.
• Speciation: Formation of new species due to barriers preventing gene flow.
• Prezygotic and Postzygotic Barriers: Prevent mating and viable offspring development.
• Allopatric, Sympatric, Parapatric Speciation: Different scenarios/speciation types based on geographic and behavioral factors.

Evidence of Evolution

• Fossil Record: Shows changes over time.
• Biogeography: Geographical species distribution.
• Embryology and Molecular Homology: Comparing embryos and DNA.

Common Ancestry

• Similar processes across organisms indicate common ancestry (e.g., glycolysis, DNA).

Continuing Evolution

• Evolution is ongoing, with genetic and fossil changes over time.
• Speciation and Morphology: New species formation and study of form and structure.

Origin of Life on Earth

• LUCA: Last Universal Common Ancestor.
• Stromatolites: Fossilized cyanobacteria mats.
• Miller-Urey Experiment: Simulated early Earth conditions showing RNA as likely first genetic material.

Source: Khan Academy and Simple Studies