Lecture Notes: 4 Forces of Evolution

Introduction

• Presenter: Andrea J. Alveshere, Ph.D., Western Illinois University
• Objective: Understanding the mechanisms of evolution through mutation, genetic drift, gene flow, and natural selection.

Evolutionary Perspective

• Modern Synthesis: Integration of Darwin’s natural selection and Mendel’s heredity.
• Population Genetics: Studies evolution at the population level, not individual.
• Definition: Evolution is a change in allele frequencies in a population over time.

Forces of Evolution

1. Mutation

• Source of Genetic Variation: Original source of genetic differences.
• Types:
  • Point Mutations: Single-nucleotide changes affecting amino acid sequences.
  • Insertions/Deletions (Indels): Additions or removals of nucleotides causing frameshifts.
  • Transposable Elements: DNA sequences that can change positions within the genome.
  • Chromosomal Alterations: Include crossover, nondisjunctions, and translocations, affecting large DNA segments.

2. Genetic Drift

• Random Changes: Changes in allele frequency due to random sampling.
• Factors:
  • Population Bottlenecks: Drastic reduction in population size reduces genetic diversity.
  • Founder Effects: New populations founded by small numbers can lead to different allele frequencies.

3. Gene Flow

• Movement of Alleles: Alleles transfer from one population to another, often through migration.
• Human Example: Admixture of different human populations.

4. Natural Selection

• Selection Pressures: Traits that confer an advantage increase in frequency.
• Types:
  • Directional Selection: Favors one extreme phenotype.
  • Balancing/Stabilizing Selection: Favors intermediate phenotypes.
  • Disruptive Selection: Favors multiple extreme phenotypes.
  • Sexual Selection: Favoring traits that increase mating success.

Special Topics

Neurofibromatosis Type 1 (NF1)

• Genetic Disorder: Autosomal dominant affecting multiple body systems.
• Symptoms: Tumors, café-au-lait spots, learning disabilities.

Sickle Cell Anemia

• Genetic Disorder: Autosomal recessive; offers malaria resistance to heterozygotes.
• Impact: Major study in balancing selection.

Studying Evolution

Hardy-Weinberg Equilibrium

• Tool for Analysis: Mathematical model for allele and genotype frequencies.
• Use: Measures if a population is evolving.

Nonrandom Mating

• Assortative Mating: Preferences based on phenotypes affecting genetic diversity.

Speciation

• Microevolution vs. Macroevolution: Small changes within species vs. new species formation.
• Speciation Types:
  • Allopatric: Due to physical barriers.
  • Sympatric: Occurs without physical separation.
  • Adaptive Radiation: Rapid diversification into new niches.

Conclusion

• Understanding evolutionary mechanisms is crucial for fields such as medicine and conservation.
• Evolutionary biology helps address challenges like antibiotic resistance and biodiversity conservation.