Answer:
Genetic drift
Step-by-step explanation:
Genetic drift can also be referred to as allelic drift, it refers to the variation in allelic frequencies within a particular population over a period of time. It can also be referred to as the random fluctuations in the number of genotypes within a population. Genetic drift is not influenced by the environment and is usually more pronounced in a small population of organisms.
For example, a population of birds can consist of green feathers and blue feathers with the green feathers as the dominant allele, but as a result of random fluctuations, the offspring may all be with green feathers and hence could eliminate or reduce the allele responsible for blue feathers over time.