7.3.8 Investigating the Effects of Random Sampling on Allele Frequencies

Key Concepts

1. Random Sampling in Small Populations:

• In small populations, random events (e.g., death of individuals, random fertilisation) can result in some alleles becoming overrepresented or lost.
• This can lead to reduced genetic diversity, which may affect the population's ability to adapt to changes in the environment.

2. Effects on Allele Frequencies:

• Genetic drift can cause allele fixation (where only one allele remains in the population) or allele extinction (where an allele is completely lost).
• This effect is less pronounced in larger populations due to a higher number of individuals carrying diverse alleles.

3. Bottleneck Effect:

• A population bottleneck occurs when a population's size is drastically reduced (e.g., due to natural disasters, disease, or human activity).
• The remaining population may have reduced genetic diversity and different allele frequencies compared to the original population.

4. Founder Effect:

• Occurs when a small group of individuals colonises a new area.
• The alleles present in the founders may not represent the full genetic diversity of the original population.

Investigating with Models and Sampling

• Practical Activity:
  • Use a simulation (e.g., beads, cards, or computer models) to represent a population with known allele frequencies.
  • Randomly sample individuals over successive generations to observe how allele frequencies change.
• Key Observations:
  • Larger populations show more stable allele frequencies due to reduced impact of chance.
  • Smaller populations display greater variation in allele frequencies due to genetic drift.