Final answer:
The heredity of Alzheimer's disease is influenced by genetic factors, with the APOE4 variant increasing risk without guaranteeing the development of the disease, making option a) the correct answer. Risk genes do not guarantee Alzheimer's, and genetic testing has both potential advantages and disadvantages.
Step-by-step explanation:
The heredity of Alzheimer's disease involves a complex interplay of genetic factors. The more common late-onset form of the disease has a genetic component, linked in part to a gene known as apolipoprotein E (APOE). Specifically, the APOE4 variant increases the risk of developing Alzheimer's but does not guarantee it, indicating that no gene acts alone in the causation of the disease. Early onset Alzheimer's, which is less common, can sometimes be caused by mutations in one of three known genes and affects a small percentage of patients. When discussing the heredity of Alzheimer's in relations such as parents and siblings, and the way genes act, it's clear that genes can increase risk but don't act in isolation or guarantee the development of the disease. Therefore, the correct answer to the question would be (a) Parents, Siblings, or Alone.
Regarding risk genes, the statement that risk genes do not guarantee a person getting Alzheimer's disease is true. Moreover, genetic testing could have advantages and disadvantages, such as providing a chance for early intervention or potentially causing unnecessary stress if the risk of developing the disease late in life is identified.