In this simulation, each black dot on a marble signifies that it has been chosen for copying (reproduction) one time. Fixation in the blue "allele" occurs within five generations..
Genetic drift is random fluctuations (or "walk") of gene frequencies from generation to generation that occur in small, isolated populations. Through genetic drift, genetic information controlling certain features may be lost from a population because it is not transmitted to the offspring. In large populations any specific trait is carried by so many individuals that unless it is unfavorable its loss is highly unlikely.