AP Daily: Hardy-Weinberg Equilibrium

Presenter: Mr. Burris

• School: Union High School, Vancouver, Washington

Today's Topic: 7.5 Hardy-Weinberg Equilibrium

Learning Objectives

1. Understand the Hardy-Weinberg model.
2. Identify conditions under which allele and genotype frequencies change.
3. Learn how to calculate allele and genotype frequencies using Hardy-Weinberg equations.
4. Recognize what changes in allele frequencies indicate.
5. Analyze the impacts on populations if Hardy-Weinberg conditions are not met.

Hardy-Weinberg Model Overview

• A model for describing and predicting allele frequencies in a non-evolving population.
• Population in Hardy-Weinberg equilibrium is not evolving; allele/genotype frequencies remain constant through generations.

Conditions for Hardy-Weinberg Equilibrium

1. Large Population: No genetic drift.
2. Absence of Migration: No gene flow.
3. No Net Mutations: Genes remain unchanged.
4. Random Mating: No sexual selection.
5. Absence of Selection: No natural selection.

• These conditions are rarely met but serve as a valuable null hypothesis.

Hardy-Weinberg Equations

1. Genotype Frequency:

   • ( p^2 + 2pq + q^2 = 1 )
     • ( p^2 ): Frequency of homozygous dominant genotype
     • ( 2pq ): Frequency of heterozygous genotype
     • ( q^2 ): Frequency of homozygous recessive genotype

2. Allele Frequency:

   • ( p + q = 1 )
     • ( p ): Frequency of dominant allele
     • ( q ): Frequency of recessive allele

Evidence of Evolution

• Changes in allele frequencies indicate evolutionary changes.
• Disruptions to equilibrium factors:
  • Mutations: Random changes in genes.
  • Non-random Mating: Selection based on traits.
  • Gene Flow: Migration affects allele frequencies.
  • Genetic Drift: Chance events in small populations (e.g., bottleneck, founder effects).
  • Natural Selection: Alleles affecting fitness and survival.

Example: Beetle Population

• Beetles in Equilibrium: Black (dominant) and red (recessive).
  • Alleles: ( A ) (Black), ( a ) (Red)
  • Allele Frequencies: ( p = 0.3 ), ( q = 0.7 )
  • Genotype Frequencies:
    • Homozygous dominant: ( p^2 = 0.09 )
    • Heterozygous: ( 2pq = 0.42 )
    • Homozygous recessive: ( q^2 = 0.49 )

Additional Practice

• Frequency calculations and implications in isolated vs. general populations.
• Example problem involving genetic drift based on allele frequencies.

Key Takeaways

1. Hardy-Weinberg models describe non-evolving populations.
2. Equilibrium conditions: large population, no migration, no mutations, random mating, no selection.
3. Use Hardy-Weinberg equations to calculate allele/genotype frequencies.
4. Changes in allele frequencies signal evolution.
5. Non-adherence to conditions can lead to population evolution, with small populations being more vulnerable.

Note: Ensure precision with decimal points in calculations.

End of Lecture Summary