The study of gene expression

Traditionally, Northern blotting was used to study gene expression using one labeled probe hybridized to an RNA target. With new high-throughput methods, in particular microarrays, the level of expression in tens of thousands of genes, in some cases the whole genome, can be visualized at once.

Expression profiling is the identification of all of the RNAs that are present in a specific tissue sample at a particular time (Cullis 2004). The simple pictoral below depicts how many genes can be analyzed at once on a microarray as compared to a very small number on a Northern blot (more about microarrays later).