We often hear about families that suffer from the same disease generation after generation. Indeed, heredity affects the body, causing certain medical tendencies or causing a disease to appear. These days we know exactly where in the genetic map are the roots of some diseases, while for others we have only an idea or know nothing at all. Deciphering the genetic code is one of the greatest challenges facing science, and the possibility of manipulating genes and avoiding diseases one of the most controversial techniques.

The genetic disorders identified so far show that there are as many as 1,110 genes which have mutated, causing a disease. There are diseases linked to the alteration of a gene, which is sometimes found on a gender-determining chromosome. There are also diseases that stem from the mutation of various genes, plus the influence of genetic factors. These diseases are hard to identify. There are also acquired genetic diseases, and some kinds of cancer are examples of these.

Problems based on the alteration of a gene include colour-blindness, cystic fibrosis, cholesterol disorters (like Hyperlipidemia)�and hemophilia A. Many hereditary diseases are recessive, which means that in order to be expressed the gene has to come from both the father and the mother. This is the case of cystic fibrosis. This is a disease characterized by defective entry and exit of chloride from the cells. This causes a sticky secretion that blocks the lungs and leads to serious respiratory problems.

Sometimes it is enough for just one of the parents to have a disease. This the case with being colour blind; the affected gene is on the X chromosome. As men have only one X chromosome, while women have two, the disease is more common in men. Hyperlipoproteinemia�affects men and women in similar proportions. Half of all immediate descendents of people with the disease are risk of having it too. The genetic mutation that causes it is known. Detecting it early is important because it is estimated that 70 percent of those with disease have a heart attack before reaching age 60.

There are many other diseases in which heredity has a major influence. One is cancer. The influence of oncogenes in the appearance of some kinds of malignant tumors is clear, such as lung cancer, although their development is clearly linked to habits such as smoking. Heredity is also at work in breast cancer. Around 90% of cases are not linked to it, but the other 10% have family-related components. These are normally the cases that show up in young women. In the same way, people who have at least two direct relatives with colon cancer also stand a greater risk of coming down with it.

Then there are cardiovascular disorders. Some of them are closely linked to�hyperlipoproteinemia�(cardiovascular accidents in young adults). As for very common type-2 diabetes, if both parents suffer from the disease, their children will also have a greater risk of having the illness. If only one of the parents is diabetic, the risk is higher if that parent is the mother. Mothers with osteoporosis and a history of fractures raise the likelihood of having daughters with the problem when they reach menopause. Scientists also know which mutated gene causes predisposition for Alzheimer, although it is known that people with this tendency will not necessarily have the disease.

In any case, always keep in mind that a healthy lifestyle, regular checkups and medical followups if there is risk of genetic disease are good tools for facing a fate that does not have to be etched in stone.