Answer:
In the founding population, the allele frequency is different from the original bigger-sized population. The size of the new population affects this difference even more. Some of the alleles will tend to increase, while some others will tend to decrease in frequency.
Explanation:
Genetic drift is an evolutive force. It is the random change that occurs in the allelic frequency of a population through generations. Its effects are harder in a small-sized population, meaning that the magnitude of this change is inversely related to the size of the original population.
Genetic drift results in some alleles loss -including the beneficial ones-, while some other alleles get fixated. Low-frequency alleles are the most likely to be lost. The changes produced by genetic drift accumulate in time and results in a loss of genetic variability within a population.
Genetic drift affects a population and reduces its size dramatically due to a disaster or pressure -bottleneck effect- or because of a population split -founder effect-. The bottleneck effect most likely affects smaller populations.
Founder effect refers to the origin of a new population from only a few individuals that are coming from a bigger-sized population. These founder individuals, which are carrying some of the genes of the original population, settle down in a new area and reproduce. The new and small population might or might not be genetically representative of the original one. Some rare alleles might be exceeded or might be lost by complete. Consequently, when the small population increases in size, it will have a genetically different composition from the original one. In these situations, genetic variability is reduced, and there exists the possibility of developing a peculiar allelic composition. When the number of individuals that originated the new population is low, the founder effect will be very extreme because the genetic drift effects are inversely proportional to the original number of individuals.
