Final answer:
Genetic drift is the random change in allele frequencies in a population, distinct from natural selection that favors advantageous traits. Events like the founder effect and bottleneck effect can lead to significant changes in a population's genetic structure based on chance alone.
Step-by-step explanation:
Genetic Drift and Natural Selection
Genetic drift is a mechanism of evolution in which allele frequencies within a population change randomly, with no advantage to the population over existing allele frequencies. This differs from natural selection, which acts on phenotypes and genotypes to favor traits that provide an advantage in survival or reproduction. While both processes usually occur simultaneously, it is challenging to discern which is more influential at any given time. Significant changes in a population's genome can result from both genetic drift and natural selection, alongside the founder effect and bottleneck effect. These effects illustrate how chance events, such as natural disasters, can substantially affect the genetic structure of a population. Genetic variation is the basis for natural selection, and when events like these occur, they can reduce variation and thus affect evolutionary processes.
Allele frequencies can also change through mutation, gene flow from migration, non-random mating based on phenotype, and the random nature of mutation and reproduction. These factors can cause deviations from the Hardy-Weinberg equilibrium and lead to microevolution. The Hardy-Weinberg Principle outlines conditions for a non-evolving population, which is rarely sustained in nature due to these evolutionary forces.