Normalization of raw data on gene expression during the cell cycle obscures the original experimental data and makes it appear as if all genes have the same numerical level of cyclical expression. Results that would not support gene expression because of minimal variations thus appear, after normalization, to be stronger than they actually are. Consideration of the effect of normalization raises critical questions about many experiments on the cell cycle dependent variation of gene expression—that is, proposed cyclical changes in mRNA content—during the cell cycle.
This paper demonstrates that normalization makes minimal variations appear much stronger than they are in the raw data, and thus one should be skeptical of some published results proposing cell-cycle specific gene expression.
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