Scientists suspect that the genes you inherit may influence how likely you are to take up risky activities, such as mountain climbing or scuba diving. Alcohol is involved in many accidents, and alcoholism has a significant genetic component. What's more, how long it takes you to recover from that meteorite injury may well depend on your genes. Your own behavior may affect when and how severely the disease strikes, however. Sickle cell attacks are more common when the body isn't getting enough oxygen, such as when exercising heavily, or living at high altitudes.
Most diseases require contributions of genetics and environment.
One example is a disease called PKU or phenylketonuria. A child cannot have PKU unless he or she inherits two copies of the defective gene, one from each parent. Before this genetic disease was well understood, children who inherited these gene variants developed severe mental retardation. Then, a few decades ago, scientists realized that the child will suffer no illness, unless he or she eats a chemical called phenylalanine. Phenylalanine is present in many, but not all, foods, and it takes knowledge and vigilance to avoid them all.