ELi5: how can a single fertlized egg/cell produce a full body with so many different cell types? are we talking about extracting a compressed file or making factories which has different products to produce?
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Factory works surprisingly well as an analogy.
Think of your DNA as the blueprint for your entire body. The fertilized embryo is essentially a command centre that tells the factory how to expand.
We want to build a human that does human things, so walking, breathing, thinking, and for that we need legs, lungs and brains. So the command centre “expands” (duplicates) and gives a copy of the blueprint to the duplicate and tells it ‘go and build a leg’ or brain etc. Essentially it is told to only work on a specific section of the blueprint. The rest is crossed out and none of its concern.
The command centre working on the leg eventually splits into command centres working on the veins, the muscles, the skin, etc, much like how in a building multiple different companies will install water and electricity, and the entire building itself of course.
Nevertheless, all of this starts with one command centre and relies on this one blueprint: Your DNA
The command centres are your so-called stem cells. Now, I should note that this seems to imply that there is one queen stem cell from which you grew, a central command centre, but this is not the case. Instead of giving out tasks which slowly grow independently, the first phases of your life you are just a clump of stem cells that can be anything.each of those then proceeds to become the sections of your body and lose their versatility, but no original stem cell can be pointed out.
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