4 months ago by
University of Cambridge, National Institutes of Health, Chapel Hill School of Medicine
Row Z-Score is a scaling method for visualization in heat maps that helps enhance clusters of genes with similar trends in expression between samples.
Z-Score is calculated by:
(Gene expression value in sample of interest) - (Mean expression across all samples) / Standard Deviation
In the heat map you show, genes with dark red are upregulated and blue downregulated. However, since the rows are Z-Score scaled, you only have information about the a single genes varying expression across the samples. Comparing the color between two separate genes cannot tell you if Gene A is more highly expressed than Gene B, however heat maps are usually not used for this purpose and instead are meant to highlight differences between samples.
This is also a previous post that is also a good explainer: https://www.biostars.org/p/159397/
Hope this helps a bit!