Evolutionary Fitness and Factors Affecting it

Introduction

• Focus on evolutionary fitness
• Factors affecting fitness and trends in evolution

Gene Flow

• Definition: Movement of gametes between populations
• Example: Birds with different dominant (blue) and recessive (red) traits migrate and mate, causing gene flow
• Effect on Population: Gene flow leads to presence of various alleles, disrupting Hardy-Weinberg equilibrium
• Outcome: Can prevent reproductive isolation and species divergence

Genetic Drift

• Definition: Random changes in allele frequency
• Types of Genetic Drift:
  • Founder Effect: Small group colonizes a new area, leading to biased allele frequencies
  • Population Bottleneck: Environmental events reduce population size drastically, changing allele frequencies
• Example: Red and yellow beans scenario

Types of Selection

Qualitative vs Quantitative Traits

• Qualitative Traits: Exist on a spectrum
• Quantitative Traits: Influenced by natural selection in various ways

Stabilizing Selection

• Definition: Reduces variation, increasing frequency of median traits (purifying selection)
• Example: Birth weight where extremes have higher mortality

Directional Selection

• Definition: Favors one end of the trait spectrum
• Example: Texas Longhorn cattle with larger horns to fend off predators

Disruptive Selection

• Definition: Favors extreme traits on both ends of the spectrum
• Example: Bird beak sizes favoring hard or soft seeds

Frequency Dependent Selection

• Definition: Distinct phenotypes benefit each other
• Example: Scale-eating fish with right and left mouthed traits

Sexual Selection

• Definition: Non-random mate selection based on traits that may not have evolutionary advantage
• Example: Bright-colored birds attracting more mates but also predators

Heterozygote Advantage

• Definition: Heterozygous genotypes have an advantage
• Example: Sickle cell allele providing malaria resistance despite its negative effects

Conclusion

• Complexity of Natural Selection: Not just survival of the fittest but involves multiple factors influencing allele persistence and frequency in populations.