A gene is a DNA or RNA sequence that carries genetic information, also called a genetic factor, and is the basic unit that controls genetic traits. Genes control the performance of traits in individual organisms by directing protein synthesis to express the genetic information they carry. Thus, children look or have a personality similar to that of their parents. Normal genes in the human body are also divided into different genotypes, or genetic polymorphisms. Different genotypes have different sensitivities to environmental factors, and sensitive genotypes can cause disease in response to environmental factors. In addition, diseases that are directly caused by abnormal genes alone are called genetic diseases. Genetic alterations are not always due to heredity. This means that genetic mutations (deletions, duplications, point mutations, etc. can be understood as genetic defects) are not always passed on to the next generation. There are three types of genetic alterations that cause disease: 1) postnatal mutations (often without a family history); 2) interactions between normal genes and the environment (often without a family history); 3) congenital defects in certain genes (often with a family history and inherited to the next generation). Diseases caused by such congenital gene defects do not result in the onset of disease in all members of the family. The onset of a genetic defect and the type of onset are determined by the function of the defective gene and how that gene is inherited. Based on the incidence in the family line, clinicians can speculate and analyze the mode of inheritance, as well as combine clinical manifestations and clinical experience to speculate which disease may be present, and perform purposeful genetic testing in tens of millions of genes. Mutations in most genes can lead to changes in the quantity or quality of functional proteins (which play important biological roles, including participation in important metabolic reactions in the body) that can cause abnormal body functions and result in disease. Genetic testing is a technique that detects DNA through blood, other body fluids or cells, and can be used to diagnose disease and also for disease risk prediction. The leap forward in molecular biotechnology has amazingly increased the speed and accuracy of genetic testing, greatly reduced the cost, and provided great convenience for clinical genetic diagnosis (diagnosis of patients and prenatal diagnosis of pregnant women).