In historical paternity testing, a direct exclusion occurred when a child expressed an antigen that he could not have inherited from the potential father or mother. An example: A group O man is the possible father of a child who is blood group AB, with a group A mother. The child’s inheritance of the B antigen is a direct exclusion of the man’s paternity, as the child has something that he could not have inherited from the purported father (or mother). Both serologic direct exclusions and indirect exclusions have been replaced by DNA-based testing methods.
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