Topic: Blood and DNA
Question: Describe the role of Blood grouping in disputed paternity and the basis for the same.
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Blood grouping can play an important role in disputed paternity cases. Here is how it works:
1. Each person inherits blood group antigens from both parents. The child’s blood group must be consistent with having inherited one antigen from each parent.
2. The allele combinations for the mother and alleged father are compared to the child’s blood group. If the alleged father cannot possibly have contributed one of the antigens that the child has inherited, then he can be excluded as the biological father.
3. There are multiple blood group systems that can be tested – ABO, Rh, MNS, Duffy, Kell, etc. The more blood group systems tested, the higher the probability of exclusion.
4. For example, if the mother is O positive and the alleged father is A positive, but the child is B positive, then the alleged father cannot be the biological father. This is because he does not carry the B antigen that the child inherited.
5. If the antigen combinations of the mother, alleged father and child are consistent with biological paternity, it does not necessarily prove paternity, but only shows that it is possible. Other evidence and testing is still needed.
6. Blood grouping has high accuracy and objectivity as evidence in disputed paternity cases. The results simply show whether the alleged father can or cannot be excluded based on inheritance of blood group antigens.
ABO blood group antigens: The ABO blood group antigens are inherited in a Mendelian fashion from the parents. A child must inherit one A or B antigen from each parent. If a suspected father does not have the necessary antigen to pass on to the child, then he cannot be the biological father.
The ABO antigens are:
– A antigen: Found on red blood cells of blood group A
– B antigen: Found on red blood cells of blood group B
– AB: Have both A and B antigens
– O: Have neither A nor B antigens
Rhesus factor: The Rhesus (Rh) factor is another inherited blood group antigen. A child must inherit the Rh factor from at least one parent. So if a suspected father is Rh negative and the child is Rh positive, he cannot be the biological father.
Other blood group systems: There are many other blood group systems like MN, Duffy, Kell etc. that show Mendelian inheritance and can be used to exclude a suspected father.
In summary, blood grouping in disputed paternity cases works by determining if the antigen combinations in the mother, alleged father and child are consistent with the alleged father passing on one antigen to the child. If an antigen inherited by the child cannot have come from the alleged father based on his blood group, he can be excluded as the biological father.
