Defining Genetic Drift
Genetic drift is the change in the frequency of an existing gene variant (allele) in a population due to random chance. Unlike natural selection, the changes from genetic drift are not driven by environmental or adaptive pressures, meaning the traits that become more common are not necessarily more beneficial.
Section 2: Key Principles
The primary principle of genetic drift is that it has a much stronger effect in small populations. In a small group, random events can easily eliminate a specific allele, whereas in a large population, the same random event would have a negligible impact on the overall allele frequency. Over time, this process can lead to the complete loss of some alleles and the fixation (100% frequency) of others, which reduces the genetic variation within the population.
Section 3: A Practical Example of Genetic Drift
Imagine a small, isolated population of wildflowers, where some have red petals (dominant allele) and some have white petals (recessive allele). If a rockslide randomly wipes out a patch of flowers that, by chance, happened to contain most of the red-flowered individuals, the next generation will have a significantly higher frequency of white flowers. This change occurred not because white flowers were better suited for survival, but purely due to a random event.
Section 4: Importance in Evolution
Genetic drift is a major mechanism of evolution that acts alongside natural selection, mutation, and gene flow. It is particularly important in population bottlenecks (when a population is drastically reduced in size) and the founder effect (when a new population is started by a few individuals). It demonstrates how evolution is not always a process of 'improvement' but can also be driven by random, non-adaptive changes.