AAT Bioquest

What happens if I add too much MgCI2 in my PCR reaction?

Posted April 27, 2023


Adding too much MgCl2 in your PCR reaction enhances enzymatic activity. This can promote non-specific binding of primers leading to errors in DNA replication. The agarose gel electrophoresis will show too many DNA bands. 

Too much MgCl2 also increases the chances of primer dimer formation. 

Adding the right MgCl2 concentration is essential to avoid getting any errors. The ideal concentration range of MgCl2 in PCR mixtures is 1.5 to 4.5 mM. A final concentration of 1.5 mM is optimal for satisfactory yield in most applications. A few may require up to 4.5 mM MgCl2. Very rarely will you need to add more.

Additional resources

Polymerase Chain Reaction: Basic Protocol Plus Troubleshooting and Optimization Strategies

Polymerase Chain Reaction (PCR)

Helixyte™ Green *20X Aqueous PCR Solution*