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When do researchers use random (mixed) base oligos? Can I get custom ratios of the random bases incorporated?

Mixed bases are used in primers to bind to templates that contain variability or a mixture of sequences at the primer binding sites. Mixed bases can also be used to create diversity in clone libraries and in site directed mutagenesis.

IDT offers random base oligos. Order them by using an upper case letter N or other IUPAC-IUB symbol. IDT offers two types of randomization, machine mix and hand mix. Machine mix bases are charged at the standard base price for the scale ordered. Hand mixing is done to provide custom ratios of the bases, and incurs an additional charge. When entering your sequence, the “Mixed Base” tab at the bottom of the page lists the IUB symbols and is where custom mix ratios need to be entered.