Expert reviewed • 08 January 2025 • 6 minute read
Population genetics involves several key forces—mutation, gene flow, and genetic drift—that interact to shape the genetic composition of populations over time. These processes can introduce new alleles, homogenise or diversify populations, and influence the course of evolution.
Only mutation can create entirely new alleles not previously present in a population. Consider a population’s gene pool like a deck of cards. A mutation introduces a novel "card," potentially altering the deck’s overall composition.
Real-world examples include the rise of pesticide resistance in insects or antibiotic resistance in bacteria. Even subtle colour variations in moths can arise from mutations, influencing survival and reproduction.
Gene flow occurs when individuals or their gametes move from one population to another, carrying genetic material with them. This migration can homogenise populations, reduce local adaptation, or increase genetic diversity, depending on the degree of gene exchange.
Mechanisms of gene flow:
The effect on variation depends on the rate of gene flow:
| Type of Gene Flow | Effect on Variation | Population Impact |
|---|---|---|
| High | Homogenises populations | Reduced local adaptation |
| Moderate | Increases variation | Enhances adaptation potential |
| Low | Allows divergence | Can lead to speciation |
Genetic drift describes random changes in allele frequencies, especially significant in small populations. Consider two main forms:
An example is the northern elephant seal population, which drastically declined in the 1890s. Although it has recovered in numbers, its genetic diversity remains very low.
These evolutionary forces rarely act alone. Mutation and drift together can quickly fix unique alleles in small populations, while gene flow and selection can combine to introduce new variants that selection then favours or removes. In small populations, drift can override selection, creating unpredictable outcomes that are vital to consider in conservation biology.
Understanding these processes aids in conservation efforts, guiding strategies to manage endangered species and ensure genetic variability. In agriculture, this knowledge informs crop improvement and pest management. In medicine, it helps predict the evolution of disease-causing organisms and the spread of drug resistance.
Collectively, mutation, gene flow, and genetic drift help shape the genetic tapestry of life, influencing adaptation, speciation, and long-term population survival.