While conducting research with a small population in South America, you note that an overwhelming majority of individuals exhibit signs of a specific genetic abnormality. What is most likely the cause of this?

Inbreeding

Explanation:

The offspring from mating of individuals in a close group can cause inbreeding. The genetic disorders present in both mates will pass along the offspring without the possibility of correction, causing genetic abnormality.

The inbreeding can occur naturally in a way to guarantee the propagation of the offspring. The result of this mating is the increasing of homozygous, which can result in lack of variancy. By the other hand, it can enhance a similar characteristic as well as a genetic problem.

For example, in a crop of clones organisms a disease which has affected one crop can spread more easily through the community of clones than non-clones crops of the same specie.

a would be the answer