What is the term for when genetic drift leads to the loss of all but one allele of a gene?

The term that describes the process by which genetic drift results in the loss of all but one allele of a gene is fixation. Fixation occurs when a particular allele becomes the sole allele present in a population for that gene, effectively resulting in the loss of genetic variation at that locus. This can happen due to random fluctuations in allele frequencies, particularly in small populations where the effects of genetic drift are more pronounced.

In essence, fixation signifies that there is no longer any alternative allele present, leading to homogeneity for that gene in the population. This phenomenon underscores the impact of genetic drift, as it operates independently of natural selection, which usually favors certain alleles over others based on their adaptive advantages. Understanding fixation is crucial in studying population genetics, as it highlights how genetic variation can diminish within populations over generations.