How do I have O positive negative blood type?
As has been said, O blood type is the standard kind of blood type you have when you have neither the A antigen nor the B antigen on your blood cells. In having neither, you develop antibodies to both. As for the rhesus (+/–) thing, you can’t be + and – for the rhesus D factor. It’s another, unrelated, antigen on blood cells which you have if you’re positive and don’t if you’re negative. There are a couple of things your +/– could mean: Firstly, our ABO type and rhesus factor are each determined by a pair of genes at one locus on a pair of your chromosomes. In the ABO case, 1A and 1B obviously yields AB type, 2Os yields O type, and the other combinations of A, B and O are either A or B type. In the rhesus factor case, there is simply a + or – gene available. So genetically you can have 2+s, 2–s or 1 of each. 1+ is sufficient to give you rhesus antigens, so whilst you’re blood is +, +/– could be your genetic type (I don’t know why they’d need to know that though). Another possibility is
