 Primers should also not anneal strongly to themselves, as internal hairpins and loops could hinder the annealing with the template DNA.When designing primers, additional nucleotide bases can be added to the back ends of each primer, resulting in a customized cap sequence on each end of the amplified region.One application for this practice is for use in TA cloning, a special subcloning technique similar to PCR, where efficiency can be increased by adding AG tails to the 5′ and the 3′ ends.