In humans, the protein CFTR regulates the components of sweat, digestive fluids, and mucus. Humans can have a normal form of the gene or a mutated form. Which of the following would provide evidence that the mutated form of the CFTR protein is harmful to humans?
a. The genetic mutation was present in all populations but did not get passed on in places where humans did not contract the disease.
b. This genetic mutation codes for the production of a protein that provides resistance to the disease.
c. The disease causes the genetic material of humans to mutate just before it causes their disease.
d. Humans with this mutation develop this disease and then spread it to other humans without the mutation.