Molecular diagnosis is a technology to make a diagnosis of human states and diseases that uses DNA and RNA as diagnostic materials and uses molecular biology techniques to detect the presence, abnormalities, or abnormal expression of genes. The basic principle is to look for changes in the structure, amount, and expression of DNA or RNA in order to see if the person has any abnormal genetic modifications, which is significant for illness prevention, prediction, diagnosis, treatment, and prognosis. In layman's words, all molecular biology-based techniques, such as PCR and gene sequencing, are molecular diagnosis techniques.
A molecular biology technology for amplification of particular DNA fragments is the PCR immunoassay, which is also called as polymerase chain reaction. The basic principle is comparable to DNA replication in nature, and it involves three main reaction steps of denaturation-annealing-extension: denaturation of the template DNA, annealing of the template DNA with the primer (renaturation), and primer extension. More "semi-retained replication strands" can be created by repeating the denaturation-annealing-extension process, and these new strands can then serve as the template for the next cycle. Each cycle takes around 2-4 minutes, and the target gene can be amplified millions of times in about 2-3 hours. The polymerase chain reaction, a basic DNA amplification process, was first proposed by Mullis in 1983 and invented by him in 1985, marking the true start of PCR technology. To put it simply, PCR is the amplification of a DNA fragment that may be identified using real-time fluorescence PCR.
A technique for determining the sequence of DNA is known as gene sequencing. The sequence analysis of DNA provides the foundation for further research and alteration of target genes in molecular biology. At present, the technologies used for sequencing mainly include the dideoxy chain end termination method invented by Sanger et al. (1977) and the chemical degradation method invented by Maxam and Gilbert (1977). Both approaches are different in principle, but they are both based on nucleotides starting at a fixed position and randomly terminating at a specified base, resulting in a succession of four groups of nucleotides of varied lengths, A, T, C and G. Electrophoresis on a urea-denatured PAGE gel detects the DNA sequence. The technique of Sanger sequencing is now widely used. Simply said, gene sequencing techniques are used to sequence and analyze DNA fragments in order to clarify the DNA sequence.
