fraction of genes up- and down- regulated

[velu]

Hi all,
In some perturbed situation (biotic, abiotic stress, etc,), are the fraction of genes up- and down-regulated are similar or can they differ so much that almost all the genes are either up- or down-regulated?

I am having RNA-seq differential analysis results that appears to be so biased towards up-regulation. Considering that the number of transcripts that a cell can make at a given time is nearly a constant, the results that I have seem to counter it.. Your inputs and clarifications are needed.
Thanks.