**7.10 Inverse PCR**

This type of PCR is used to detect the sequences that surround the target DNA (flanking sequences). It involves a series of restriction enzyme digestions and self-ligation. The primers amplify sequences at either end of the target by extending outward from the known DNA segment [4, 7, 51].

## **7.11 Reverse transcription-PCR (RTP)**

In this technique, the PCR is preceded by a reaction converting RNA into cDNA using viral reverse transcriptase. The resulting cDNA is used as a template for a second conventional PCR. The technique is widely used in the detection of RNA viruses and to study gene expression [7, 52, 53]. A variant of the RTP, called differential-display reverse transcription-PCR or RNA arbitrarily primed PCR (RAP-PCR), is used to study and compare the gene expression of organism grown under different conditions. The variant employs the use of short and random 10-mer or 11-mer radio-labeled primers that are annealed at low stringency conditions to promote the extension of random sequences during the first PCR cycle. This is followed by high-stringency cycles to extend the products of first cycle. The resulting products are analyzed using standard sequencing gels, and RAP-PCR fingerprints are visualized by autoradiography. The technique is extremely useful in studying tissue-specific and condition-specific gene expressions [54, 55].
