ELI5- What are blood groups? Why do they differ from person to person? Why can’t a person of one blood group receive blood from a person of a different blood group?

Question

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In: Biology

Answer 1

Your blood cells have little markers on them that say ‘I belong to this body’

If you give someone blood with the wrong tag, then your immune system starts attacking the other person’s blood thinking it’s an invader causing an allergic reaction. Which is bad.