Genetic testing (also called DNA-based tests) is among the newest and most sophisticated of techniques used to test for genetic disorders which involves direct examination of the DNA molecule itself. Other genetic tests include biochemical tests for such gene products as enzymes and other proteins and for microscopic examination of stained or fluorescent chromosomes. Genetic tests are used for several reasons, including:

• carrier screening, which involves identifying unaffected individuals who carry one copy of a gene for a disease that requires two copies for the disease to be expressed
• preimplantation genetic diagnosis (see the side bar, Screening Embryos for Disease)
• prenatal diagnostic testing
• newborn screening
• Genealogical DNA test (for genetic genealogy purposes)
• presymptomatic testing for predicting adult-onset disorders such as Huntington's disease
• presymptomatic testing for estimating the risk of developing adult-onset cancers and Alzheimer's disease
• confirmational diagnosis of a symptomatic individual
• forensic/identity testing