Genetics and Medicine: an evolving relationship.

The rapid expansion of knowledge in human and medical genetics has revealed at least 6 percent average heterozygosity per structural gene locus, in excess of 2300 Mendelian (single gene) variants and several hundred chromosomal variants in man. This means that with the exception of monozygous twins, no two individuals are alike in their phenotype. Therefore, each person has a relative state of health, and genetic factors contribute significantly to disease. The ubiquity of genetic diversity requires the development of services for genetic screening, diagnosis, and counseling to prevent and treat a major portion of disease in modern society. Specific programs in Quebec and Canada illustrate how individuals and populations can be served by such services. Better education of citizens and health professionals in human genetics is essential for the further improvement of genetics services in society.