O blood group do not have antigens but it possess antibodies is called universal donar because it don't have antigens ,so the recipient body don't release any antibodies which prevent the agglutination of blood .
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The blood group O has no antigen because it acts as a universal donor which don’t have any antigen. That’s the reason it also don’t produce antibodies in the recipient body. So it’s clear that it can be denoted to anyone.