Mutations occur all the time, but cells have the ability to recognize mistakes and fix them before it passes it on to its descendent cells. But the repair system can fail or become less efficient with age. Over time mutations accumulate. More mutations makes it more likely that genes that code for the structure and function of proteins will be affected, leading to possible disease. Many human diseases are inherited through dominant, recessive and complex modes.
Dominant genes prevail over normal copies.
Dominant inheritance means that one copy of an abnormal gene is enough to cause disease. Huntington's disease is an example of a dominant disorder where everyone with the abnormal gene has the disease. Recessive Inheritance Recessive inheritance means that two abnormal copies of the gene must be present for the individual to be affected. An example of a recessive disorder is cystic fibrosis. Cystic Fibrosis is a disease that impairs breathing and digestion.