MgCl2 is an essential reagent in the polymerase chain reaction (PCR) as it plays a critical role in the amplification process.

MgCl2 functions as a cofactor for Taq polymerase, which is the most commonly used DNA polymerase in PCR. It is required for the activity and stability of Taq polymerase, which extends the primers and synthesizes new DNA strands during PCR. MgCl2 also helps to stabilize the double-stranded DNA (dsDNA) and promotes the annealing of the primers to the template DNA.

The concentration of MgCl2 in the PCR reaction is critical, and it can affect the specificity and yield of the PCR product. The optimal MgCl2 concentration varies depending on the specific PCR reaction conditions and the DNA polymerase used. It is recommended to optimize the MgCl2 concentration in the PCR reaction to achieve the best results.