Made One
What prevents every protein that your DNA codes for from being made in every one of your cells?
You know how all of your DNA is in each of your cells. What prevents every protein that your DNA codes for from being made in every one of your cells?
What makes the genes turn on and off?
Different genes are turned on and off in different cells.
For example liver cells have different genes turned on and working than in stomach cells and kidney cells which have their own specific genes turned on and working.