Genetic testing, also known as DNA testing, allows the genetic diagnosis of vulnerabilities to inherited diseases, and can also be used to determine a child’s parentage (genetic mother and father) or in general a person’s ancestry or biological relationship between people. In addition to studying chromosomes to the level of individual genes, genetic testing in a broader sense includes biochemical tests for the possible presence of genetic diseases, or mutant forms of genes associated with increased risk of developing genetic disorders. Genetic testing identifies changes in chromosomes, genes, or proteins. Most of the time, testing is used to find changes that are associated with inherited disorders. The results of a genetic test can confirm or rule out a suspected genetic condition or help determine a person’s chance of developing or passing on a genetic disorder. Several hundred genetic tests are currently in use, and more are being developed. Because genetic mutations can directly affect the structure of the proteins they code for, testing for specific genetic diseases can also be accomplished by looking at those proteins or their metabolites, or looking at stained or fluorescent chromosomes under a microscope. This article focuses on genetic testing for medical purposes. DNA sequencing, which actually produces a sequences of As, Cs, Gs, and Ts, is used in molecular biology, evolutionary biology, metagenomics, epidemiology, ecology, and microbiome research.