Natural selection

• Genetic diversity


  The number of different alleles of genes in a population
• Natural selection can only occur if there is genetic diversity
• Natural selection


  A process where the end result is evolution
• Evolution


  The change in allele frequency over many generations in a population
• Antibiotic resistance in bacteria

  • Different levels of resistance represented by different colors
  • Original population had a range of resistance alleles
  • After selection, only two resistance alleles remained
  • Over generations, the proportion of the two alleles changed
• Types of adaptations


  • Anatomical (structural features)
  • Physiological (chemical reactions)
  • Behavioral (how organism behaves)
• Process of natural selection

  1. Genetic diversity caused by random gene mutations

  2. New advantageous alleles allow individuals to survive and reproduce more

  3. Advantageous alleles increase in frequency over generations
• Fur color in mice


  • Genetic diversity in fur color
  • Dark fur color is selectively advantageous
  • Dark fur allele increases in frequency over generations
• Vision ability in owls


  • Good vision is selectively advantageous
  • Owls with good vision are more likely to survive and reproduce
• Directional selection


  One of the extreme traits has the selective advantage, due to a change in the environment
• Stabilizing selection


  The modal (middle) trait has the selective advantage, when there is no change in the environment
• Human birth weight


  • Very low or very high birth weights are disadvantageous
  • Average birth weights are selectively advantageous
• The process of natural selection is the mechanism by which evolution occurs.
• Variation refers to differences between individuals within a population that can be passed on from one generation to another through reproduction.
• Inheritance involves passing genetic information from parents to offspring during sexual reproduction.
• Selection refers to differential survival and reproductive success among individuals based on their phenotypes.
• Adaptations are physical or behavioral characteristics that increase an organism's chances of surviving and reproducing in its environment.
• Adaptations are traits that increase an organism's chances of surviving and reproducing in its environment.