Two identical cells under the same environmental conditions still show differences in their makeup due to ‘developmental noise’ which we currently can’t totally control.
Stochastic expression, in simple terms, means random variation. Levels of mRNA in cells can fluctuate over time due to transcription occurring in bursts rather than continuously, the availability of transcription factors, and extracellular signalling. This noise can lead to fluctuations in the levels of proteins in a cell, variation that could be crucial in determining the fate of a cell in development. The intrinsic stochastic nature of gene expression requires an understanding of the different types of random noise that will be present in the process. Some of these will be significant in changing the fate of a cell whereas others will not.