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

Alright so imagine that every town has a gang. Some gangs are Crips (type A), some towns are Bloods (type B), and some towns are just ruled by local small-time gangs (type O). Everyone wants to defend their turf, so Crips will straight up murder any Bloods they see in their town and vice versa. Some towns are contested (type AB) so Crips AND Bloods can operate there. The local gangs don’t really have a side in the Crip/Blood feud so they can actually operate on anyone’s turf. But they also don’t want Crips or Bloods muscling them out so they will waste any Crips or Bloods that show up on their turf.