The founder effect is an important cause of genetic drift in addition to natural selection and random drift. The founder effect is the difference between the gene pool of a population as a whole and that of a newly isolated population of the same species. The founder effect occurs when populations are started from a small number of pioneer individuals of one original population. Because of small sample size, the new population could have a much different genetic ratio than the original population. An example of the founder effect would be when a plant population results from a single seed.