What is the term for genetic change due to chance that can lead to one allele being lost?

Genetic drift refers to the random changes in allele frequencies in a population, particularly in small populations, due to chance events. This process can lead to the loss of alleles over time, as certain alleles may become fixed (reach a frequency of 100%) while others may be completely lost. This concept is particularly significant because it emphasizes that the changes in genetic variation can occur independently of natural selection, meaning that the effects are random rather than driven by adaptive advantage. Over successive generations, genetic drift can have a profound impact on the genetic diversity of a population, which is crucial for understanding evolutionary processes.

This differs from the other terms provided; for instance, gene flow involves the transfer of alleles between populations, potentially increasing genetic variation rather than causing a loss. Mutation refers to changes in the DNA sequence that can introduce new alleles, while selection pressure pertains to environmental factors that can influence the survival and reproductive success of individuals based on their phenotypic traits. Each of these processes has distinct implications for population genetics, making genetic drift a unique and essential mechanism of evolutionary change.