A mother whose blood type AB has a child who is AB also. A potential father is blood type O. A well-informed geneticist concludes that (1) He cannot be the father (2) He might be the father (3) He is very likely to be the father (4) He or any other male of blood type O could be the father

NEET Class neet Answered

Asked by prakriti12oct | 31 Oct, 2019, 08:20: PM

Expert Answer

We know that ABO blood group system is controlled by a gene which has 3 different forms denoted by the symbols I^A, I^B and I^O.
The genes I^A and I^B show no dominance over each other, i.e. they are co-dominant. However I^A and I^B both are dominant over the gene I^O. This means that I^O is recessive in relation to genes I^A and I^B.
Now, coming to our question, the blood group of the woman is AB, which means the woman has gene combination I^AI^B.
The blood group of the child is also AB, which means the child has gene combination I^AI^B.
Now, from the rules of inheritance of blood groups, the blood group of the child can determined depending on the blood groups of the mother and the father.
But we already know that A and B are codominant and they both are dominant over O. This implies that the child receives one dominant copy of gene from mother and one from the father.
Hence, the father needs to have atleast one copy of A or B. However, the potential father has blood group O, which means that his genetic combination is I^OI^O, where both alleles are recessive.
This will not be the case and hence, the father with blood group O cannot be the father of the child with blood group AB and mother with blood group AB.

Answered by Sheetal Kolte | 01 Nov, 2019, 11:13: AM