Answer:
Founder effect.
Explanation:
Founder effect is a case of genetic loss due to an event in which a small subset of individuals of a population becomes isolated from a larger population. As the problem states, this population will never represent the diversity existing in the original larger population, and without the opportunity to interbred with a different population, this group will become distinct.
One of the reported outcomes of the founder effect is the explanation of the higher prevalence of some genetic disorders in specific populations.