Cellular noise

Cellular noise is random variability in quantities arising in cellular biology. For example, cells which are genetically identical, even within the same tissue, are often observed to have different expression levels of proteins, different sizes and structures. These apparently random differences can have important biological and medical consequences.

Cellular noise was originally, and is still often, examined in the context of gene expression levels – either the concentration or copy number of the products of genes within and between cells. As gene expression levels are responsible for many fundamental properties in cellular biology, including cells' physical appearance, behaviour in response to stimuli, and ability to process information and control internal processes, the presence of noise in gene expression has profound implications for many processes in cellular biology.

The most frequent quantitative definition of noise is the coefficient of variation:

where ${\displaystyle \eta _{X}}$ is the noise in a quantity ${\displaystyle X}$, ${\displaystyle \mu _{X}}$ is the mean value of ${\displaystyle X}$ and ${\displaystyle \sigma _{X}}$ is the standard deviation of ${\displaystyle X}$. This measure is dimensionless, allowing a relative comparison of the importance of noise, without necessitating knowledge of the absolute mean.

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