The correct answer is: B. genetic drift.
Genetic drift is the change in the frequency of a gene variant (allele) in a population due to random sampling of organisms. The smaller the population, the greater the effect of genetic drift. This is because in a small population, there is a greater chance that a particular allele will be lost or become fixed (i.e., present in all individuals in the population).
Gene flow is the movement of genes from one population to another. This can happen through migration, interbreeding, or the exchange of gametes. Gene flow can help to reduce genetic drift by increasing the genetic diversity of a population.
Natural selection is the process by which organisms that are better adapted to their environment are more likely to survive and reproduce. This can lead to changes in the frequency of alleles in a population.
Mutation is a change in the genetic material of an organism. Mutations can be caused by errors in DNA replication, exposure to radiation or chemicals, or viruses. Mutations can be beneficial, harmful, or neutral.
In a small population, genetic drift is more likely to occur than in a large population. This is because in a small population, there is a greater chance that a particular allele will be lost or become fixed (i.e., present in all individuals in the population). Gene flow, natural selection, and mutation can also occur in small populations, but they are less likely to have a significant impact on the population’s genetic diversity.