A person can have normal chromosomes in number and structure, but still have a disease or condition caused by a mutation in one or more of the genes on the chromosomes. A single gene defect usually does not cause the chromosome structure or number to be abnormal.
Explanation:
I'm not sure if this is correct but hope it helps.
The answer is A the central nervous system sends a message to the brain and then peripheral nervous system sends out the message to react. I think hope I helped
