Hardy-Weinberg Equilibrium

May 30, 2024

Hardy Weinberg Equilibrium Lecture Notes

Introduction

Key Points

  • Math is integral in biology (e.g., Chi squares, osmotic pressure, Punnett squares).
  • Hardy Weinberg (HW) Equilibrium combines biology and math.

Definition of Hardy Weinberg Equilibrium

  • Allele and genotype frequencies in a population remain constant unless evolutionary forces act upon them.
  • Population: Group of same-species organisms that can interbreed and have fertile offspring.

Assumptions for Hardy Weinberg Equilibrium

  1. No Selection: No natural selection impacting reproductive fitness based on traits.
  2. No Mutation: Genes are inherited without mutations.
  3. No Migration: No organisms entering or leaving the population.
  4. Large Population: Sufficiently large to avoid genetic drift.
  5. Random Mating: Mating occurs without preference.

Real-Life Applications

  • HW Equilibrium is rare in nature due to evolutionary forces (e.g., predation based on traits).
  • Value lies in providing a baseline to compare evolving populations.

HW Equilibrium Equations

Allele Frequencies

  1. Equation: p + q = 1
    • p: Dominant allele frequency in the population.
    • q: Recessive allele frequency in the population.
    • Important: p and q don't have to be equal; dominant alleles aren't always more common.

Genotype Frequencies

  1. Equation: p² + 2pq + q² = 1
    • p²: Frequency of homozygous dominant (GG).
    • 2pq: Frequency of heterozygous (Gg).
    • q²: Frequency of homozygous recessive (gg).

Example Problem

Given Data

  • New population: 500 frogs
    • 375 dark green frogs
    • 125 light green frogs

Steps to Solve

  1. Determine Equation: Given genotypes (HW second equation).
  2. Frequency Calculation of Known Genotype:
    • Light green (gg) frogs: 125/500 = 0.25
    • q² = 0.25
  3. Solve for q:
    • q = √0.25 = 0.5
  4. Solve for p using p + q = 1:
    • p = 1 - 0.5 = 0.5
  5. Calculate Genotype Frequencies:
    • p² = 0.25 for GG.
    • 2pq = 0.5 for Gg.
    • q² = 0.25 for gg.

Final Tips

  1. Calculations: Use calculators and expect rounding for more complex problems.
  2. Check Results: Ensure values sum to 1 for both equations.
  3. Avoid Assumptions: Only work with known frequencies where appropriate.
  4. Practice: More practice leads to better understanding and application.

Remember, Hardy Weinberg Equilibrium provides a crucial baseline for studying evolutionary forces.