Question

Blood groups of a couple are AB and O. The possible blood group of children would be

• A. O group only
• B. AB blood group
• C. A or B
• D. AB and O

Answer 1

The correct option is C A or B

Human blood group inheritance is the example of codominance and multiple alleles. It is governed by three alleles namely I${}^A$, I${}^B$ and i. I${}^A$ and I${}^B$ show codominance while allele "i" is recessive to both "I${}^A$" and "I${}^B$". Genotypes of a parent with “AB” blood group is “I${}^A$ I${}^B$” and that of with “O” blood group is “ii”. The AB parent forms two types of gametes; 50% with “$I^A$” and 50% with “I${}^B$” while the parent with O blood group produces one type of gamete with “i” allele. The possible genotypes by the combination of “I${}^A$”, “I${}^B$” and “i” are “I${}^A$i” and “I${}^B$i”. Allele "i" is recessive to both "I${}^A$" and "I${}^B$" thus “I${}^A$i” and “I${}^B$i” express A and B blood group respectively. To have a child with O blood group, both parents should have at least one I${}^O$ allele; this makes options A and D wrong. To have a child with AB blood group, one parent should have at least one I${}^B$ allele and other at least one I${}^A$ allele; this makes option B wrong. The correct answer is C.