Editing Northern blot (section)

==Reverse northern blot ==
Researchers occasionally use a variant of the procedure known as the reverse northern blot.  In this procedure, the substrate nucleic acid (that is affixed to the membrane) is a collection of isolated DNA fragments, and the probe is RNA extracted from a tissue and radioactively labelled.
The use of [[DNA microarray]]s that have come into widespread use in the late 1990s and early 2000s is more akin to the reverse procedure, in that they involve the use of isolated DNA fragments affixed to a substrate, and hybridization with a probe made from cellular RNA.  Thus the reverse procedure, though originally uncommon, enabled northern analysis to evolve into [[expression profiling|gene expression profiling]], in which many (possibly all) of the genes in an organism may have their expression monitored.