It is the area of biology concerned with the study of inheritance, or heredity, the process by which certain characteristics of organisms are handed down from parent to offspring. Modern genetics began in 1865. Genetics is especially relevant to humans because a large proportion of human disease and ill health has a genetic basis. Hereditary disease is passed on from generation to generation because of defective genes, and genetic defects in individual cells are the real cause of cancers. A massive research program is under way to fully characterize the complete human gene set.
Heredity plays a major role in human susceptibility to many illnesses.
Approximately one in every 35 babies is born with a genetic disorder or birth defect. Genetic diseases appear later in the lives of another one in 50 people. Diagnostic and predictive genetic testing is increasingly being used to identify individuals at risk for developing late-onset genetic diseases, such as certain forms of cancer, heart disease, and neuromuscular disorders. The individual may then use specialized testing, preventive therapy, or a change in lifestyle to alter their risk. In same cases this information may influence the individuals reproductive choices.