Our genetic make-up (genotype) contributes to many common diseases, for example our vulnerability to diabetes and heart disease. Environmental factors, however, also have their effect. Knowing about the genetic contribution to our vulnerability to disease helps us to avoid problems by taking account of the environmental factors within our control. In the cases of diabetes and heart disease for example, a sensible diet helps increase our chances of reaching a ripe old age (page 68).

Medical genetics establishes the genetic basis of disease and guides the treatment of people with genetic disorders. It also provides the data which inform potential parents about the genetic risks of starting a family.

Any prospective or expectant parents who have reason to be worried about genetic disorders that their future children might inherit can receive genetic counselling (page 99). During genetic counselling, statistical evidence and results from amniocentesis, chorionic villus sampling (page 90) or other techniques are discussed by a trained genetic counsellor with the couple concerned. The counselling helps couples make informed choices about whether to start a family if there is a chance of them having children with genetic disorders. It also helps expectant mothers and their partners to decide whether to continue with a pregnancy when they know their baby has a genetic disorder.

Techniques

Before continuing you need to remember that:

• Genes are carried on chromosomes which form pairs during meiosis. The two chromosomes of a pair are called homologous chromosomes. […]