Lecture Notes: Introduction to Hardy Weinberg Equilibrium
Overview
- Common misconception: No math in biology
- Importance of math in biological concepts: Chi squares, osmotic pressure, Punnett squares, etc.
- Focus: Hardy Weinberg Equilibrium
Definition
- Named after a mathematician and a physician
- Principle: A population’s allele and genotype frequencies remain constant unless influenced by evolutionary forces
- Population: Group of the same species that can interbreed
Assumptions for Hardy Weinberg Equilibrium
- No selection: No natural selection impacts reproductive fitness
- No mutation: Inherited genes are stable with no mutations
- No migration: No influx or exit of individuals in the population
- Large population: Minimizes the impact of genetic drift
- Random mating: No specific mate selection
Application and Relevance
- Hardy Weinberg Equilibrium provides a baseline for comparing evolving populations
- Helps to determine the impact of evolutionary forces
Key Equations
Allele Frequency Equation
- p + q = 1
- p: Dominant allele frequency
- q: Recessive allele frequency
- Dominant allele doesn’t need to be more common
Genotype Frequency Equation
- p² + 2pq + q² = 1
- p²: Homozygous dominant frequency (GG)
- 2pq: Heterozygous frequency (Gg)
- q²: Homozygous recessive frequency (gg)
Example Calculation
- New population of 500 frogs: 375 dark green, 125 light green
- Steps to solve:
- Use second equation for genotypes
- Calculate recessive genotype frequency (q² = 0.25 → q = 0.5)
- Calculate dominant allele frequency using p + q = 1 (p = 0.5)
- Determine genotype frequencies using p² + 2pq + q² = 1
- p² = 0.25 (GG)
- 2pq = 0.5 (Gg)
- q² = 0.25 (gg)
Tips for Solving Hardy Weinberg Equations
- Use a calculator for complex numbers
- Ensure results sum to 1 for accuracy
- Avoid assumptions, especially with dominant phenotypes
- Practice extensively, use online resources
Reminder: The Hardy Weinberg Equilibrium is a crucial tool for understanding evolutionary biology.