Discuss the advantages of PCR in comparison to southern blotting.
Both PCR and Southern Blotting are used to detect for the presence of a specific DNA sequence. In PCR, the sequence of interest is amplified through the use of a DNA polymerase and sequence specific primers. An agarose gel is often used to visualize the presence of an amplified sequence, seen as a band of distinct size on a gel. In Southern Blotting, the sample would be run through a gel, immobilized on a membrane, then probed to detect a band of distinct size on the membrane. Often, radioactivity is used for visualization.
There are several advantages to using PCR. First, PCR is much more sensitive because it will amplify the target sequence such that it becomes the most abundant species in the sample. Theoretically, the amplification fold is 2 to the power of (number of cycles), since the amount of DNA is doubled for each PCR cycle. Second, PCR has become so routine that almost all molecular biology labs are equipped to carry it out. The reagents necessary are relatively inexpensive and safe, compared to Southern Blotting, where special probes (often radioactive) have to be acquired and specialized equipment for working with radioactive substances are needed.