AP Daily Video Topic 7.2: Natural Selection

Presenter: Tanaya Hibbler

• Works at Brophy College Preparatory, Phoenix, Arizona.
• Encouragement: "You can do this!"

Key Learning Points

• Importance of phenotypic variation in a population.
• Natural selection’s action on phenotypic variation.
• Impact of changing environments on selective pressures.
• Variables influencing an organism's fitness.

Genetic and Phenotypic Variation

• Genetic Variation:
  • Describes genotypic and phenotypic differences in a population.
  • Leads to different phenotypes/adaptations via natural selection.
  • Individuals with favorable traits have higher survival and reproduction chances.
• Role in Survival:
  • Increases probability of population survival under changing conditions.
  • Specific phenotypes may become advantageous with environmental changes.

Selective Pressures

• Definition: Abiotic/biotic factors affecting survivability (e.g., disease, predation, climate, food).
• Adaptations can be selected for or against based on environmental conditions.
• Fitness is relative to environmental conditions.
  • Changing conditions can switch which phenotypes are advantageous.

Example: Peppered Moths in England

• Phenotypic Variation:
  • Moths varied in color (light vs. dark).
  • Post-Industrial Revolution: Dark moths camouflaged better, increased in population.
  • Post-Clean Air Act: Lighter moths became more common again.

Fitness and Reproductive Success

• Definition of Fitness: Reproductive success over generations.
• Phenotypes that decrease survival/reproduction negatively impact fitness.
• Phenotypes that increase survival/reproduction positively impact fitness.

Example: DDT Resistance in Insects

• DDT Resistance:
  • DDT used as insecticide, banned in the U.S. in 1972.
  • Natural variation led to DDT-resistant insects surviving and reproducing.
  • Resistant populations can form in 2-20 years.

Concept Explanation Practice

• Biological concepts/processes explanation practice.
• Example: Sickle cell trait frequency linked to adaptation and selective advantage.

Takeaways

• Phenotypic variation increases population survival in unstable environments.
• Natural selection selects individuals with advantageous traits.
• Environmental changes affect which traits are selected for or against.
• Phenotypes enhancing survival/reproduction significantly increase fitness.