From the sequencing of the human genome, we believe that there are approximately 21,000 protein-coding genes in the genome, of which 1500-3000 are transcription factors. If every gene has a tissue-specific and signal-dependent transcription pattern, how can such a small number of transcriptional regulatory proteins generate a much larger set of transcriptional patterns?

The best answer to the question: If every gene has a tissue-specific and signal-dependent transcription pattern, how can such a small number of transcriptional regulatory proteins generate a much larger set of transcriptional patterns? Would be:

Because transcriptional regulators, which are the ones responsible for initiating, and stopping, transcription of RNA into protein, often work in pairs, one goes with the other, and thus increase the regulatory capabilities over gene expression so that the genes translated into RNA and then transcribed into aminoacids in protein chains, actually code for the correct protein types.

These regulators will both stand, as appropriate, on a specific gene to promote its transcription, or prevent it, depending on the different signaling mechanisms received.