The activation of the molting gene in insect larvae is controlled by a hormone which activates a regulatory protein on the gene. Albumin synthesis in bird eggs is promoted by an estrogen-protein complex that binds near the enhancer region of the albumin gene. The androgen receptor in human males is essential for testosterone to function. Most chromosomes have regions that are very tightly condensed. Transcription can not take place in these regions.
Females have two X-chromosomes.
In cells, one of them is deactivated and tightly condensed, the so-call Barr body, in which no transcription occurs. The choice of which X gets condensed for a given cell line appears to be random. As you can see, there is much work yet to be done in this field, and the possibilities are endless for what we, as humans, might obtain from on-going research. DNA is far from the molecule that Watson and Crick first described.