Answer:
The correct answer will be option- E
Explanation:
The founder effect is the effect observed on the gene pool when a new isolated population is founded by the individuals migrated from the larger population. After migration, they inbred among them which changes the genetic pool of the small population.
In the given question since the population of the small town remained isolated from the American population and inbred among them, therefore, changed the genetic pool of the population.
Thus, the founder effect is the correct answer.