Genetic research has found several genes that either cause hereditary disease or predispose to disease. Today, about 5,000 diseases caused by a single gene are known.

These genes can be either dominant or recessive. They can also be sex-linked and jump over generations. Thus, the inheritance of genes may not always be quite as simple and schematic as shown in the examples above.

Genes can influence the prevalence of various illnesses, such as coronary artery disease, allergies, asthma and certain types of cancer. Fortunately, the onset of these diseases can be influenced by your lifestyle choices.

Human health is affected by heredity and the environment. For example, getting the flu can be prevented with good hygiene.