In-Depth Notes on Natural Selection and Evolution for AP Biology Exam Preparation

Overview of Natural Selection

• Focus of Session: Preparation for AP Biology exam, specifically Unit 7 content, which is extensive and crucial for success.

Introduction to Natural Selection

• Concept Origin: Developed by Charles Darwin during his voyage on the SS Beagle.
• Key Idea: Descent with modification - organisms evolve over time through changes in traits that enhance survival.
• Mechanism: Favorable traits lead to better survival and reproduction rates, increasing allele frequency in the population over generations.

Examples of Natural Selection

• Peppered Moth:
• Light and dark color variation.
• Industrial Revolution led to darker trees; dark moths thrived while lighter moths were preyed upon, increasing the frequency of dark moths.
• Antibiotic Resistance:
• Non-resistant bacteria die off, allowing resistant strains to survive and reproduce.

Misconceptions in Evolutionary Theory

• Lamarckian Theory Misunderstanding:
• Lamarck proposed that traits acquired during life could be passed on. (E.g., cutting off an ear would not cause offspring to lack ears).
• Emphasis on genetic change being necessary for trait inheritance.

Artificial Selection vs. Natural Selection

• Artificial Selection: Human-directed breeding for desired traits (e.g., dog breeds).
• Natural Selection: Traits favored by the environment without human intervention (e.g., bacteria developing resistance).

Types of Natural Selection

1. Disruptive Selection:

• Favors extremes over the intermediate (e.g., large and small beak birds thrive while medium beak birds decline).

1. Stabilizing Selection:

• Favors the intermediate trait (e.g., birth weights of humans around 6-8 pounds).

1. Directional Selection:

• Favors one end of the spectrum (e.g., increased horse size due to strength requirement).

Hardy-Weinberg Principle

• Conditions for Equilibrium:

1. Large population size
2. Random mating
3. No mutations
4. No gene flow (migration in or out)
5. No natural selection

• Formula: P² + 2PQ + Q² = 1; where P = frequency of dominant allele, Q = frequency of recessive allele.
• Evolution Indication: Change in allele frequencies signals that evolution is occurring.

Genetic Drift Facts

• Two types:
• Founder Effect: Small population established away from larger population leads to non-representative allele frequencies.
• Bottleneck Effect: Sharp reduction in population size due to environmental events affects allele frequencies randomly.
• Allele Frequency Change: Indicates evolution.

Phylogenetics and Speciation

• Phylogenetic Trees vs. Cladograms:
• Visual representations showing evolutionary relationships, based on genetic data and characteristics.
• Types of Speciation:
• Allopatric: Geographic barriers lead to speciation.
• Sympatric: Speciation within the same geographic area due to behavioral, temporal or habitat isolation.

Reproductive Isolation Mechanisms

• Prezygotic Barriers: Prevent mating/fertilization (e.g., behavioral, temporal, mechanical isolation).
• Postzygotic Barriers: Impact viability/ fertility of hybrids (e.g., hybrid inviability, infertility like mules).

Evolutionary Evidence

• Biochemical Evidence: DNA and protein comparisons show evolutionary relationships.
• Morphological Evidence: Physical traits similarity and differences may not always indicate common ancestry due to convergent evolution.
• Analogy vs. Homology: Analogous structures arise from convergent evolution without common descent (e.g., sugar gliders vs. flying squirrels).

Study Strategies for AP Biology Exam

• Daily Review: Check resources like Instagram and various YouTube channels.
• Practice FRQs and MC Questions: Key to understanding exam format and improving scores.
• Conceptual Understanding: Focus on core concepts and how they interrelate, using both practice and review materials.
• Mock Exams: Essential for assessing knowledge and identifying weak areas.

Conclusion

• Continuous learning and application of concepts crucial for mastery of the subject. Utilize various resources for effective review as exam approaches.
• Stay engaged, practice regularly, and reach out with questions for clarification.