AP Biology Unit 7: Evolution

Introduction

• Evolution is a major theme in AP Biology, dealing with changes over hundreds of millions to billions of years.
• Key topics: Selection, Population Genetics, Hardy-Weinberg Equilibrium, Speciation, Extinction, Phylogeny, Origin of Life.

Types of Selection

1. Natural Selection

• Developed by Charles Darwin.
• Involves inherited variation, survival, and reproduction of individuals with advantageous traits.

2. Artificial Selection

• Also known as selective breeding.
• Breeders select for desired traits over generations.
  • Examples: Brassica oleracea species (cauliflower, broccoli) and dog breeds.

3. Sexual Selection

• Selection for traits increasing reproductive success.
• Intersexual Selection: Mate choice (e.g., female turkeys choosing males).
• Intrasexual Selection: Competition among males (e.g., elephant seals).

Types of Selection Effects

• Directional Selection: Favors one extreme phenotype.
• Stabilizing Selection: Favors average phenotypes (e.g., birth weight in humans).
• Disruptive Selection: Favors both extremes over average phenotype.
• Adaptive Melanism: Darkening in response to environmental changes (e.g., rock pocket mice).

Population Genetics and Hardy-Weinberg Equilibrium

• Study of gene distribution and change over time.

• Gene Pool: All alleles in a population.

• Hardy-Weinberg Principle: Allele frequencies remain constant unless influenced by evolutionary factors.

  • Conditions: No mutation, large population, random mating, no migration, no selection.

• Population Genetics Equations:

  • p + q = 1
  • p² + 2pq + q² = 1

Genetic Drift and Gene Flow

• Genetic Drift: Random changes, significant in small populations.

  • Population Bottleneck: Drastic reduction in numbers, reduces genetic diversity.
  • Founder Effect: New populations started by a few individuals differ genetically from source populations.

• Gene Flow: Movement of alleles between populations.

Mutation

• Source of genetic variation.
• Can change allele frequencies if directional.

Evidence for Evolution

• Homologous Structures: Indicative of common ancestry (e.g., vertebrate limbs).
• Vestigial Structures: Structures with no apparent function, inherited from ancestors.
• Analogous Structures: Similar function, different evolutionary origin (e.g., wings of insects and birds).
• Molecular Homologies: Genetic similarities (e.g., hemoglobin in vertebrates).
• Embryology: Similarities in embryo development across species.
• Biogeography: Geographic distribution of species.
• Fossils and Dating:
  • Relative Dating: Based on position in sedimentary layers.
  • Absolute Dating: Based on radioactive decay.

Speciation

• Biological Species Concept: Groups of interbreeding natural populations.

• Reproductive Isolating Mechanisms:

  • Prezygotic Barriers: Prevent mating or fertilization.
  • Postzygotic Barriers: Reduced hybrid viability/fertility.

• Modes of Speciation:

  • Allopatric Speciation: Geographical isolation.
  • Sympatric Speciation: Occurs without geographical barriers.

Extinction

• Normal Extinction: Gradual loss of species.
• Mass Extinction: Rapid and widespread loss, often due to catastrophic events.
• Human Impact: Contributing to sixth mass extinction through habitat destruction and introduction of invasive species.

Phylogeny and Cladistics

• Phylogenetic Trees: Show evolutionary relationships.
• Clades: Groups including an ancestor and all its descendants.
• Molecular Clocks: Estimate divergence times based on mutation rates.

Origin of Life

• Life's emergence involved forming simple molecules that became more complex without enzymatic action.
• Miller-Urey Experiment: Demonstrated abiotic synthesis of organic molecules.
• RNA World Hypothesis: Suggests RNA as the first genetic material.

These notes provide an overview of Unit 7: Evolution in an AP Biology course, covering essential concepts and processes related to biological change over time, the mechanisms driving these changes, and the evidence supporting the theory of evolution.