Hardy-Weinberg Model Assumptions and Genetic Drift

Importance of Large Population Size

Assumption: The Hardy-Weinberg model assumes a large population.
- Reason: In large populations, chance events have minimal impact on allele frequencies.
Small Population Impact:
- If the population is small (e.g., 10-20, 50-100, or even a few hundred individuals), allele frequencies are likely to change over time due to chance.
- Example: Biodiversity lab simulation using coin tosses to represent meiosis and random mating without selection.
  - Small populations may not achieve a 50/50 ratio due to chance.
  - Larger populations (e.g., 1,000 students) have outcomes closer to expected ratios due to larger sample size.

Definition: Genetic drift refers to changes in allele frequencies due to chance, particularly in small populations.
Random Walk Analogy:
- An allele's frequency may fluctuate randomly if there's no selection acting on it, similar to a drunk person unable to control their direction on a platform.
- Eventually, an allele will become fixed or eliminated over time.
Influence of Population Size:
- Small populations equate to a narrow platform, leading to quicker fixation or elimination of alleles.
- Larger populations provide more leeway, delaying fixation or elimination.
Allele Frequency's Role:
- Initial allele frequencies affect probability of fixation or elimination.
- Example: A 95% allele is more likely to be fixed, while a 5% allele is more likely to be eliminated.
- Random events in a small population can still alter expected outcomes.

Definition: A 'deem' is a small sub-population within a larger population.
- More likely to interbreed within itself than with the larger population.
- Allele frequencies can be affected differently within a deem compared to the larger population.