Question

Blood group of a mother is A, that of son is B. What is the blood group of father_______________?
A. B
B. A
C. O
D. None of the above

Answer 1

Hint:- Blood type in humans is determined by codominant allele. Each biological parent donates their ABO allele (one out of two) into their offspring. For ABO, the different genotypes are AA, AO, BB, BO, AB and OO.

Complete step-by-step solution:-
Karl Landsteiner, a biologist discovered the blood group A, B and O. The fourth group AB was later discovered by another research team. The concept of blood typing is used to determine paternity by excluding some men from being the father. Red blood cells have a chemical substance, which is known as antigen, on their surface. The ability of the formation of these antigens is governed by genes that are inherited by the mother and father of an individual. The pattern of genes is known as genotype and its physical appearance is known as phenotype. Genotype decides the phenotype. For e.g. if a father and mother have blood group O, then the child must have O type only. Here is a table to define the possibility of a blood group in a child based on his/her parents.

Mother’s blood type	Father’s blood type	Mother’s genotype	Father’s genotype	Child blood group
A	A	AA, AO	AA, AO	A, O
A	B	AA, AO	BB,BO	A, AB, B, O
A	AB	AA, AO	AB	A, AB, B
A	O	AA, AO	OO	A, O

After this observation, we can clearly get an idea about the possible blood group. If a mother is having A blood type and her son has B blood type then the possible blood type of father could be B or AB.
So, the correct answer is A.

Note:- The test to identify the blood group is known as ABO typing. Blood is mixed with antibodies against the blood group. Person having blood group A contains B-Antibody, same as with B blood group.