Vaccines. Sometimes the patient may be allergic and can not handle the small dose.
Answer:
Mutations
Explanation:
A gene mutation is a permanent change in the DNA sequence of a gene. Mutations can occur in a single base pair or in a large segment of a chromosome and even span multiple genes. Mutations can result from endogenous (occurring during DNA replication) or exogenous (environmental) factors.
Estrogen is a hormone that fight heart disease that post menopausal women don't have anymore