A poorly chosen oligonucleotide can turn a well-planned experiment into weeks of troubleshooting. Failed PCR, weak hybridization, off-target amplification, and low cloning efficiency can all be the result of a improperly designed oligos. The right choice depends on the experiment, the target sequence, the chemistry required, and the downstream method. Oligo selection is a critical part of experimental design, not just a final ordering step. Oligo choice starts with matching t