Final answer:
The high incidence of certain rare genetic diseases in the Amish can be explained by bottlenecks and inbreeding. Therefore, the correct option is D.
Step-by-step explanation:
The correct answer is (D) a and b are correct. The high incidence of certain rare genetic diseases in the Amish can be explained by a combination of bottlenecks and inbreeding.
By having a small population size and limited gene pool, the Amish community has experienced genetic bottlenecks, where a significant portion of the genome is lost. This can lead to the concentration of rare, deleterious mutations that cause harmful phenotypes.
In addition, inbreeding among close relatives in the Amish community increases the likelihood of rare recessive disease-causing alleles being inherited. This can result in a higher incidence of certain rare genetic diseases.