The amish population who migrated from europe to the united states had very few individuals in their population. additionally, their gene pool shows very few alleles due to inbreeding. a genetic trait called polydactyly (having six fingers), which is rare in other populations, is common amongst them. what kind of evolutionary effect is exhibited in this example?

The Amish have a genetic trait called polydactyly which is rare among other populations of people. This means that a person can 6 fingers, usually an extra thumb. This kind of evolutionary effect that is exhibited in this specific example is called the Founder effect. This happens when there is a small number of colonizing ancestors. 

So, the founder effect since it refers to migrating population.