Lecture Notes: Evolution of Populations

Introduction

• Focus on 5 mechanisms of evolution: Mutations, Gene Flow, Non-Random Mating, Genetic Drift, and Natural Selection.
• Emphasis on how natural selection leads to speciation.
• Darwin's theories validated by modern research, yet he was unaware of genetics.
• Importance of DNA sequencing in understanding evolution.

Key Concepts

Variation in Populations

• Genetic variation originates from mutations.
• Variations must confer differences in reproductive success (fitness).
• Variations must be heritable.

Mechanisms of Evolution

1. Mutations

   • Introduce new alleles, affecting allele frequency.
   • Rates are low but crucial for natural selection.

2. Gene Flow

   • Movement of alleles between populations.
   • Can homogenize populations or introduce new alleles.

3. Non-Random Mating

   • Can alter allele frequencies.
   • Examples: sexual selection, geographical isolation.

4. Genetic Drift

   • Changes in allele frequencies due to chance.
   • More impactful in small populations.
   • Two types: Bottleneck Effect and Founder Effect.

5. Natural Selection

   • Primary mechanism for evolution.
   • Differential survival and reproduction based on phenotype.
   • Influences include pesticide resistance and antibiotic resistance.

Types of Natural Selection

• Disruptive (or Diversifying) Selection: Favors extreme traits over intermediates.
• Directional Selection: Favors one extreme trait over others.
• Stabilizing Selection: Favors intermediate traits and reduces extremes.

Population Genetics

• Hardy-Weinberg Principle: Used to determine if a population is in genetic equilibrium.
  • Formula: p^2 + 2pq + q^2 = 1
  • p and q represent allele frequencies.

Speciation

• Process: Formation of new species from ancestral species.
• Types:
  • Adaptive Radiation: Rapid evolution into various species.
  • Prezygotic and Postzygotic isolation mechanisms.

Prezygotic Isolation

• Temporal, habitat, and behavioral isolations.

Postzygotic Isolation

• Hybrid viability and sterility.

Large Scale Evolutionary Concepts

• All living organisms share common genetic material, suggesting a shared ancestor.
• RNA world hypothesis: RNA as the original genetic material.

Conclusion

• Evolution driven by natural selection is a gradual process.
• Speciation and genetic divergence occur over long timescales.

Recommended Viewing

• Documentary on Natural Selection narrated by David Attenborough.