system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: how does DNA “know” when to do what?

If the DNA is a recipe to making a person, how does the DNA “know” that when you’re a child it shouldn’t produce a full size femur bone or foot or anything? How is it timing when we grow?
gpt
The DNA doesn't "know" it's forming a bone. It includes the when and how, but not the end result.

Random example: the gene that is needed to form a hand is in every single cell. But the corresponding protein (wich has the name "sonic hedgehog" for whatever reason) is only created when the conditions are right, wich is - because of other DNA - only the case twice (once at each arm, in week X of pregnancy).

If you artificially duplicate the protein you can make additional hands, but only at the end of a limb, not everywhere (has been experimentally shown in animal tests)

So the "cooking recipe" includes the when and how, and kind of forms a chain of that. As a methaphor for a cake it would say something like "add an egg whenever there is a 50/50 mix of flour and milk" and the previous steps have to make sure those conditions are met some time.