BIOL 108 Introduction to Biological Diversity

Topic 7: Evolution of Population

Overview of Evolutionary Changes

• Macroevolution:
  • Evolutionary change above the species level.
  • Examples include phenotypic variations like coat colors.
  • Populations evolve under natural selection pressure, not individuals.
  • Population is the smallest unit of evolutionary change.
• Microevolution:
  • Evolutionary change below the species level.
  • Change in allele frequencies over generations.

Basic Genetics Terminology

• Chromosome: Structure carrying genetic material.
• Gene: Unit of hereditary information.
• Alleles: Alternative gene versions that differ in nucleotide sequences.
  • Each parent contributes one chromosome to offspring.
  • Alleles typically remain separate unless there is incomplete dominance.

Microevolution in Populations

• Gene Pool: Sum of all alleles in a population.
  • Geographical separation can result in distinct gene pools.
• Genotypic Variation: Provides material for natural selection.
  • Essential for evolution.

Sources of Genotypic Variation

• Mutations:
  • Random changes in genetic makeup.
  • Can be beneficial, neutral, or harmful.
  • Only heritable if occurring in gamete-producing cells.
• Gene Duplication: Copying of genetic sequences.
• Recombination: Shuffling of alleles during sexual reproduction.

Factors Influencing Allele Frequencies

• Natural Selection:
  • Acts on genetic variations.
  • Can lead to adaptation through different selection types:
    • Directional: Favors one phenotypic extreme.
    • Disruptive: Favors both phenotypic extremes.
    • Stabilizing: Favors intermediate phenotypes.
• Genetic Drift:
  • Random allele frequency changes.
  • Greater impact on smaller populations.
  • Includes bottleneck and founder effects.
• Gene Flow:
  • Transfer of alleles between populations.
  • Can introduce new variations and counteract genetic drift.

Evolutionary Changes

• Driven by selection, drift, and flow.
• Extinction: Complete species loss.
• Extirpation: Local extinction.

Maintaining Genotypic Variation

• Balancing Selection:
  • Maintains genetic diversity.
  • Heterozygote Advantage: Heterozygotes have adaptive advantages.
  • Frequency-dependent Selection: Fitness depends on phenotype frequency.

Limitations of Natural Selection

• Adaptations only need to be sufficient, not perfect.
• Natural selection lacks ultimate goals and acts on existing variations.
• Environmental changes influence selection processes.

References and case studies from various studies and articles provide illustrations and deeper understanding of the concepts discussed.