Certain traits will have been lost from the gene pool forever. some may be obvious, like people with red hair or double jointed thumbs. others will be less obvious, like the ability to process cholesterol or being allergic to peanuts.
This loss of diversity in a reduced population is called ________.

A. gene flow
B. bottleneck effect
C. genetic drift
D. founder effect

The situation described in the question is an example of the founder effect. It can be described as "when a small amount of people leave their habitats and form a smaller population elsewhere, there is a decrease in genetic diversity and this change is called the founder effect."

"In a reduced population" in the question points to the founder effect. Although if the reduction of the population is dramatic and immediate, it can also be an example of the bottleneck effect.

I hope this answer helps.