Hardy-Weinberg Model Assumptions and Genetic Drift

Large Population Assumption

• Reason for Large Population: In large populations, chance events do not significantly impact allele frequencies.
  • Small populations (10-20, 50-100, even a few hundred) have more fluctuation in allele frequencies due to chance.

Simulation Example

• Population Genetic Simulation:
  • Coin tossing represents meiosis and random mating.
  • Small group outcomes vary widely (not always 50-50 heads/tails).
  • Larger groups (e.g., 1000 students) have outcomes close to expected ratios due to large sample size.

Genetic Drift

• Definition: The effect of chance on allele frequency in small populations.
  • Also known as a "random walk."
  • Neutral alleles (no selection impact) fluctuate randomly.
  • Over time, alleles become either fixed or eliminated.

Random Walk Analogy

• Analogy: A drunk walking randomly on a platform.
  • Narrow Platform: Small population, allele fixation or elimination occurs quickly.
  • Wide Platform: Larger population, takes more time for fixation or elimination.

Factors Affecting Allele Outcomes

• Current Allele Frequency: Influences probability of fixation or elimination.
  • Example: 95% of one allele is more likely to be fixed compared to 5%.

Concept of Deems

• Definition: A deem is a small sub-population.
  • More likely to interbreed within the deem than with the larger population.
  • Allele frequencies can differ within a deem compared to the overall population.