The term diagnosis refers to the detection of disease. When the disease is detected, it can be cured then only. This technique is used in biotechnology. With the help of molecular diagnostics, we can determine the nature and the cause of the disease. This can be done by evaluating the patient’s history and by the examination of the laboratory data. The polymerase chain reaction that is PCR is a method of diagnostics. It helps to detect very low levels of bacteria or virus at the time when their symptoms are not available. It is also used to identify genetic disorders. It can also be used to detect mutations in cancer patients.