Gene expression value

Question

[dadiwi8427]

What does the gene expression value tell you? what does it mean if it's greater than 1 or less than 1?

Answer 1

[seidel]

A gene expression value is a proxy meant to convey something about the concentration of a transcript in a cell. Larger numbers mean higher abundance, lower number mean lower abundance. There are no meaningful absolute values, so your question about less than 1 or greater than 1 does not really mean anything, without knowing where that number came from, or what kinds of units are involved.

Another common form of gene expression value refers to a log2 ratio of a given gene between two conditions. For instance, cells exposed to a drug or not. Such an experiment might result in a gene expression value giving the ratio of expression between treatment and control (no treatment). It's common to use log2 scale for this because a gene which does NOT respond to treatment, and is thus at equal concentration in the cell under both conditions, would have a 1/1 ratio, or log2 value of 0. (log2 of 1 is zero). Whereas a gene induced 2 fold by drug treatment would have a log2 value of 1 (if 2 fold = 2/1 expression ratio of treatment/control, the log2 of 2 is equal to 1). And conversely, if the the gene is 2-fold less abundant in treatment than control, treatment/control = 1/2, the then log2 value would be -1. This is convenient because fold changes up or down become equidistant from 0, which is good for visualization, plotting, calculating distances for clustering, etc.

Answer 2

[swbarnes2]

A number with no unit or context doesn't tell anyone anything.