The correct answer is a) founder effect.
Genetic drift refers to the random changes in allele frequencies within a population, which can lead to significant evolutionary changes over time, particularly in small populations. The founder effect is a specific type of genetic drift that occurs when a small group of individuals becomes isolated from a larger population and establishes a new population. This new population may have different allele frequencies than the original population simply due to the limited genetic diversity of the founders.
In contrast, gene flow (option b) involves the transfer of alleles between populations, and mutation (option c) refers to changes in the DNA sequence that create new genetic variations. Both of these processes are important in evolution but are not considered examples of genetic drift.
Thus, the founder effect serves as a classic illustration of genetic drift in action.