AP Biology Unit 7: Evolution

Welcome to the climax of the AP Biology course focusing on the vast and intricate topic of evolution. This unit covers the biological evolution spanning billions of years and explains changes through time.

Key Topics

• Selection: Natural selection, artificial selection, sexual selection
• Population Genetics: Hardy-Weinberg equilibrium
• Evidence for Evolution
• Speciation and Extinction
• Philogyny (Phylogeny)
• Origin of Life

Selection

Natural Selection

• Developed by Charles Darwin in the 1800s.
• Built upon the idea of artificial selection.
• Natural selection involves variation, inherited traits, and differential survival and reproduction.
• Examples include adaptations like sonar in bats and camouflage in geckos.

Artificial Selection

• Also known as selective breeding.
• Breeders select desired traits over generations.
• Examples include the Brassica oleracea plant family (cauliflower, broccoli, etc.) and dog breeds.

Sexual Selection

• Traits that increase reproductive success.
• Types:
  • Intersexual Selection: Female choice; e.g., tail feathers in turkeys and peacocks.
  • Intrasexual Selection: Male competition; e.g., size and aggression in elephant seals.

Types of Selection

• Directional Selection: Shifts phenotype distribution.
• Stabilizing Selection: Selects against extremes; e.g., birth weight in babies.
• Disruptive Selection: Selects for both extremes.
• Adaptive Melanism: Darkening in response to environmental changes.

Evolutionary Fitness

• Definition: Survival and propagation of genes through offspring.
• Demonstrated in penguin life cycles and evolutionary adaptations.

Hardy-Weinberg Equilibrium

• Population Genetics: Study of gene distribution in populations.
• Key Equations:
  • p + q = 1
  • p² + 2pq + q² = 1
• Misconception: Dominant alleles don't necessarily mean more common.
• Factors Violating Equilibrium:
  • Small populations, natural/sexual selection, gene flow, directional mutation.

Genetic Drift

• Random Change: Usually in small populations.
• Bottleneck Effect: Drastic reduction in population size.
• Founder Effect: New population founded by a small number of individuals.

Gene Flow

• Movement of alleles between populations.
• Can involve individuals or gametes.

Mutation

• Source of genetic variation.
• Can be directional, affecting allele frequencies.

Speciation and Extinction

Biological Species Concept

• Defines species based on natural interbreeding and viable, fertile offspring.
• Limitations: Hybridization, asexual/extinct species.

Reproductive Isolating Mechanisms

• Prezygotic: Prevent zygote formation.
• Postzygotic: Hybrid inviability or sterility.

Modes of Speciation

• Allopatric: Geographic isolation.
• Sympatric: Non-geographic isolation, often in plants or due to microhabitat adaptation.
• Adaptive Radiation: One species radiates into multiple with unique adaptations.

Evidence of Evolution

Homologous Traits

• Shared structures from a common ancestor.
• Example: Animal forelimbs.

Vestigial Structures

• Inherited structures with no apparent function.

Analogous Features

• Similar function, different structure.
• Convergent Evolution: Independent evolution of similar features.

Molecular Homologies

• Genetic similarities indicating common ancestry.

Fossils

• Show change over time and transitional forms.
• Relative Dating: Based on superposition.
• Absolute Dating: Using radioactive decay (e.g., carbon-14).

Evolution Continued

• Evolution observable in phenomena like resistance in mosquitoes to DDT, antibiotic resistance in bacteria.

Philogyny (Phylogeny)

Phylogenetic Trees

• Show evolutionary relationships based on morphological and genetic evidence.
• Key Concepts:
  • Clade: Common ancestor and all descendants.
  • Shared Derived Characters: Traits distinguishing a clade.
  • Molecular Clocks: Using mutation rates to estimate divergence times.

Origin of Life

Steps of Origin

• Habitability of Earth
• Abiotic synthesis of monomers and polymers
• Formation of protobionts
• Emergence of self-replicating cells (RNA world hypothesis)

Miller-Urey Experiment

• Simulated early Earth conditions to produce amino acids.

This comprehensive unit covers the fundamental principles of evolutionary biology and prepares students for advanced understanding and application in AP Biology exams.