Genetic engineering revolutionizes and expands the study of genetic disease. As a consequence, a growing number of conditions of the human body and mind are the subject of gene analysis, genetic testing, and genetic screening. Areas of application include prenatal diagnosis of embryos and fetuses during pregnancy, screening of newborn infants, and screening of children and adults. There has been an increase in the number and range of genetic diagnostic tests for inherited traits and diseases, and for predispositions to certain noninherited diseases such as some forms of cancer. The expansion of genetic testing on embryos, fetuses, children, and adults has legal, medical, employment, and reproductive implications.
Before the 1970s, there were only three ways to diagnose diseases known or thought to be inherited: (1) through the study of inheritance patterns by observing which members of a family were affected, (2) by taking blood samples to diagnose conditions with biochemical (mostly protein) tests, (3) by looking under a microscope for structural abnormalities of the cells and chromosomes. Chromosomes are the threadlike structures in the nucleus of a cell where the genes are packaged. They are large enough to be observed under a microscope.
Genetic engineering changed the scope of genetic diagnosis. Now it is possible to isolate and manipulate genes (pieces of DNA) to study relationships between genes and physical characteristics. The same technology is