Notes on Natural Selection and Evolution for AP Biology Exam

Unit 7: Natural Selection

7.1 Introduction to Natural Selection

• Enduring Understanding: Evolution changes the genetic makeup of a population over time and is supported by multiple lines of evidence.
• Learning Objective: Describe the causes of natural selection.
  • Natural selection is a major mechanism of evolution (EVO-1.C.1).
  • Darwin’s theory posits that competition for limited resources leads to differential survival; individuals with favorable phenotypes are more likely to survive and reproduce (EVO-1.C.2).

Key Concepts

• Evolutionary Fitness: Measured by reproductive success (EVO-1.D.1).
• Environmental Stability: Both biotic and abiotic factors can be stable or fluctuating, influencing evolution (EVO-1.D.2).

7.2 Natural Selection

• Learning Objective: Describe the importance of phenotypic variation in a population.
  • Natural selection acts on phenotypic variations (EVO-1.E.1).
  • Changes in environments impose selective pressures (EVO-1.E.2).
  • Certain variations increase/decrease fitness significantly in specific environments (EVO-1.E.3).

Illustrative Examples

• Changes in flowering time (Plant A and B).
• Peppered moth coloration in response to industrial pollution.
• Sickle cell anemia and its relation to malaria resistance.

7.3 Artificial Selection

• Learning Objective: Explain how humans can affect diversity within a population.
  • Through artificial selection, humans influence variation in species (EVO-1.F.1).
• Learning Objective: Explain the relationship between environmental changes and evolutionary changes.
  • Convergent evolution occurs under similar selective pressures, resulting in similar adaptations (EVO-1.G.1).

Key Concepts

• Artificial vs. Natural Selection: Domestication processes differ from taming individual wild species.

7.4 Population Genetics

• Learning Objective: Explain how random occurrences affect population genetic makeup (EVO-1.H).
  • Mutations, genetic drift (bottlenecks, founder effect), and gene flow are key processes.

Important Terms

• Bottleneck Effect: A significant reduction in population size leads to reduced genetic variation.
• Founder Effect: A small group starts a new population, leading to limited genetic diversity.

7.5 Hardy-Weinberg Equilibrium

• Learning Objective: Describe the conditions under which allele and genotype frequencies change in populations (EVO-1.K).
  • Hardy-Weinberg conditions: large population, no migration, no mutations, random mating, no selection (EVO-1.K.1).
  • Hardy-Weinberg Equation: p² + 2pq + q² = 1 (allele frequency calculations).

Application

• Predicting allele frequencies in a non-evolving population and understanding evolutionary evidence through observed deviations.

7.6 Evidence of Evolution

• Learning Objective: Describe types of data providing evidence for evolution (EVO-1.M).
• Evidence from various scientific disciplines supports evolutionary theory.

Key Data Types

• Fossils and dating methods, molecular comparisons, morphological homologies, and vestigial structures.

7.7 Common Ancestry

• Learning Objective: Describe structural and functional evidence supporting common ancestry across domains (EVO-2.B).
• Shared molecular processes and structures reinforce the concept of common descent.

7.8 Continuing Evolution

• Learning Objective: Explain ongoing evolution in living organisms (EVO-3.A).
  • Populations are continuously evolving (EVO-3.A.1).
  • Resistance evolution in pathogens illustrates this process.

7.9 Phylogeny

• Learning Objective: Describe evidence types used to infer evolutionary relationships (EVO-3.B).
  • Phylogenetic trees and cladograms illustrate relationships and speciation.
  • Molecular data confer greater accuracy than morphological traits in establishing relationships.

7.10 Speciation

• Learning Objective: Describe conditions for new species to arise (EVO-3.D).
  • Speciation occurs through reproductive isolation and other mechanisms.

7.11 Extinction

• Learning Objective: Describe factors leading to extinction of populations (EVO-3.G).
  • Extinctions have historical occurrences and implications, often accelerated by environmental stress (EVO-3.G.1).

7.12 Variations in Populations

• Learning Objective: Discuss genetic diversity's role in ecological resilience (SYI-3.D).
  • Populations with low diversity are more susceptible to environmental pressures; high diversity improves resilience.

7.13 Origins of Life on Earth

• Learning Objective: Describe scientific evidence supporting life origin models (SYI-3.E).
  • Various hypotheses about life origins are supported by geological evidence and experimental findings, such as Miller-Urey.

Final Concepts

• Life's complexity arose from simple chemical processes and the development of self-replicating molecules (RNA world hypothesis).

Additional Topics for Review

Cladograms and Phylogenetic Trees

• Understand how to read and interpret cladograms and phylogenetic trees, which depict evolutionary relationships among species.

Hardy-Weinberg Equilibrium

• Use the Hardy-Weinberg equation to determine if a population is in equilibrium based on conditions (large population, no migration, no mutations, random mating, no selection).

Natural Selection Pressures

• Explain how environmental pressures (biotic and abiotic) influence natural selection by imposing selective pressures on phenotypic variations, resulting in differential survival and reproduction.

Types of Selection

• Sketch and interpret graphs of:
  1. Directional Selection
  2. Stabilizing Selection
  3. Disruptive Selection

Evidence of Natural Selection

• Identify and provide five pieces of evidence supporting natural selection:
  1. Fossil records
  2. Comparative anatomy
  3. Molecular biology
  4. Observational studies on natural populations
  5. Experiments demonstrating changes in populations over generations.

Pre-Zygotic Barriers

• Name examples of pre-zygotic barriers that prevent hybrid formation:
  • Temporal isolation
  • Behavioral isolation
  • Habitat isolation
  • Mechanical isolation
  • Gametic isolation

Post-Zygotic Barriers

• Name examples of post-zygotic barriers and their functions:
  • Hybrid inviability
  • Hybrid sterility
  • Hybrid breakdown

Bottleneck Events and Founder Effect

• Discuss how bottleneck events (significant reduction in population size) lead to reduced genetic variation, while the founder effect (small group establishes a new population) can lead to limited diversity.

Speciation Types

• Differentiate between allopatric speciation (geographic isolation) and sympatric speciation (speciation without geographic separation, often through reproductive isolation mechanisms).

This comprehensive study guide encompasses all essential information you need to excel in your understanding of evolution and natural selection for your exam preparation.