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    so i was doing the may 2007 paper 1 test for some revision and this was one of the questions:


    What feature demonstrates co-dominance in the inheritance of ABO blood groups?
    A. When A antigens and B antigens are present on red blood cells.
    B. When A antibodies and B antibodies are present in blood serum.
    C. When IA and i alleles are expressed in homo-zygotes.
    D. When IA and i alleles are expressed in hetero-zygotes.

    i put down the answer as B but the mark scheme says its A.

    can someone please tell me why? i thought antigens were foreign bodies to which the immune system would send out a response to, and that the antibodies in the blood would reflect the alleles that make up the blood type?
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    Well, I guess it could have easily been named after the antibodies instead, then what is now O blood type would be AB and so on. So I think this is more of a naming convention, like how conventional current was decided to be in the opposite direction of the flow of electrons.

    But since blood group is defined by the antigens present on the red blood cell, then A would be the answer, because it shows the co-dominance where both A and B antigens are present.

    And also I don't think antigen necessarily means it is from a foreign substance. I think as long as it can elicit an immune response of antibody production it is an antigen.
 
 
 
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