Why do we have different blood group?
Answers
bcoz r parents r different
There are four main blood types. Blood type A is the most ancient, and it existed before the human species evolved from its hominid ancestors. Type B is thought to have originated some 3.5 million years ago, from a genetic mutation that modified one of the sugars that sit on the surface of red blood cells. Starting about 2.5 million years ago, mutations occurred that rendered that sugar gene inactive, creating type O, which has neither the A or B version of the sugar. And then there is AB, which is covered with both A and B sugars.
These sugars are what makes some blood types incompatible: if blood from a type-A donor were given to a person with type-B, the recipient's immune system would recognize the foreign sugars as an invader and cue an attack. The resulting immune reaction can kill. Type O-negative blood is known as the "universal donor" because it lacks the molecules that would provoke that reaction (the "negative" means it lacks another type of surface molecule, known as the Rh antigen).
But incompatibility is not part of the reason humans have blood types, says Harvey Klein, chief of transfusion medicine at the National Institutes of Health Clinical Center. "Blood transfusion is a recent phenomenon (hundreds of years, not millions), and therefore had nothing to do with the evolution of blood groups," he said.
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