Figure 1.
RT–PCR primers are chosen in adjacent exons, with the predicted product spanning an intronic splice site. In this way, should any genomic DNA persist in the RNA preparation, any amplification from genomic DNA will produce a long product (A), containing both the targeted sequence and intervening intron. Amplification from mRNA (B) will produce only a short product as the intronic sequence has been spliced out of the mRNA.
