Definition
Gene regulation is the cell's control system for deciding when a gene is switched on, in which tissues, and at what intensity. If a gene is the recipe, regulation is the kitchen manager who decides whether to cook it, how many portions, and at what time of day.
For Sapolsky this is the conceptual hinge of the whole nature-versus-nurture debate. The dramatic part of the genome is not the genes themselves but the surrounding regulatory regions — and those regions are the points where the environment makes contact with DNA.
Why it matters
How it works
Each gene is flanked by stretches of regulatory DNA — promoters and enhancers — that act as docking sites. Transcription factors, themselves proteins, bind these sites and either recruit or block the machinery that copies the gene into RNA. Environmental signals such as stress hormones change which transcription factors are active, so an external event is converted, step by step, into a shift in how the genome is read.