why do all cells in a body have to have a copy of the whole DNA?

Question

For example why does a skin cell has a copy of how to make blood cells if their only job is just to do skin cell things?

In: Biology

Answer 1

Because humans “happend to be” the way we are.
You are right that its completely unnecessary for all cells to have a complete DNA.

However humans (like other multicellular beings) were originally made by copiees of the same cell doing different things – and “erasing” the unnecessary code precisely – while keeping whats necessary – is more effort than “just copy everything and disregard what isnt important to you”.