Although BLOOD GROUP STUDIES cannot be used to prove paternity, they can provide unequivocal evidence that a male is not the father of a particular child. Since the red cell antigens are inherited as dominant traits, a child cannot have a blood group antigen that is not present in one or both parents. For example, if the child in question belongs to group A and both the mother and the putative father are group O, the man is excluded from paternity. The picture below shows the phenotypes (observed characters) of the offspring that can and cannot be produced in the matings on the ABO system, considering only the three alleles (alternative genes) A, B, and O. Similar inheritance patterns are seen in all blood group systems.

https://www.britannica.com/science/blood-group/Paternity-testing
https://www.nature.com/scitable/topicpage/paternity-testing-blood-types-and-dna-374/#:~:text=In%20cases%20of%20questioned%20paternity,to%20all%20of%20his%20offspring.
therefore with as low as 1k, a blood group system testing can proove with absolutely certainty that a man is NOT the father of a child, however if the child blood group shows some match, then a step should be taken further for DNA test

it can show one i not the father but cant proove you are the father?? ayam confuse
well with this development no hiding place for them women, those lots will all be exposed