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. Diagnostic testing: Diagnostic testing is used to diagnose or rule out a specific genetic or chromosomal condition. 2  In many cases, genetic testing is used to confirm a diagnosis when a particular condition is suspected based on physical mutations and symptoms.