ttp://en.wikipedia.org/wiki/Inosine#Biotechnology
When designing primers for polymerase chain reaction, inosine is useful in that it will indiscriminately pair with adenine, thymine, or cytosine. This allows for design of primers that span a single nucleotide polymorphism, without the polymorphism disrupting the primer's annealing efficiency.
ttp://www.dartmouth.edu/~ambros/protocols/other/koelle/degenerate_PCR.html
2) the use of inosine as a "neutral" base
Inosine is a purine (which occurs naturally in tRNAs) that can form base pairs with cytidine, thymidine, and adenosine (although the inosine:adenosine pairing presumably doesn't fit quite correctly in double stranded DNA, so there may be an energetic penalty to pay when the helix bulges out at this purine:purine pairing). Recently, most people have been using inosine in their primers at positions where any of the four bases might be required. Each use of inosine thus reduces the degeneracy of the primer pool 4-fold. |
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