Allele Frequencies of Geographically Isolated Populations
Definition
Allele frequency
Allele frequency refers to how common a particular allele is within a population. It is expressed as a proportion or percentage of all alleles for a specific gene.
- When populations are geographically isolated, allele frequencies, this shows how common specific genetic variants are and how they change over time.
- This process can lead to unique traits or even new species.
In a population of 100 individuals (200 alleles total), if 60 alleles are a specific variant, the allele frequency is 60/200 = 0.30 or 30%.
Isolation Drives Changes in Allele Frequencies
Geographic isolation prevents populations from interbreeding, leading to changes in allele frequencies through the following mechanisms:
- Genetic Drift Creates Random Changes: Random events in small populations can dramatically shift allele frequencies.
- Natural Selection Shapes Traits: Different environmental pressures favor specific alleles, leading to adaptation.
- Mutations Introduce New Alleles: Unique mutations arise in isolated populations, contributing to genetic diversity.
- Founder Effect Alters Starting Frequencies: When a small group establishes a new population, its allele frequencies often differ from the original population.
Human Example: Alcohol Metabolism Genes Vary by Region
The ADH1B gene, which encodes an enzyme that breaks down alcohol, shows striking differences across populations.
Key Alleles of ADH1B
- ADH1B*1: Associated with slower alcohol metabolism.
- ADH1B*2: Associated with faster alcohol metabolism and reduced risk of alcoholism.
Geographic Distribution
- ADH1B*2 is common in East Asia but rare in Europe.
- This may have been favored in regions where rice cultivation led to increased alcohol consumption. Faster metabolism reduced the negative effects of alcohol.
