Expression Profiling, Functional Genomics, Global Expression Profiling, Cellular Phenotypes, Biological Phenomena

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	Expression Profiling- Determination of the cell types/tissues in which a gene is expressed as well as when (e.g., the developmental stage or the external stimulus) the gene is expressed is called expression profiling. In functional genomics, the aim is to study the expression pattern of (Ideally) all the genes present in the genome at the same time; this is called global expression profiling.
This can be done either at the RNA level or at the protein level. At the RNA level, one could use either direct sequence sampling or DNA arrays (Appendix-2.XII); the latter are described in some detail here. At the protein level, one may use either two-dimensional electrophoresis, followed by mass spectrometry or protein arrays. Global expression profiling provides insights into complex biological phenomena, including differentiation, response to stress, onset of a disease, etc. It also provides a new way to define cellular phenotypes; this, in turn, could reveal novel drug targets and help develop more effective drugs.