A married couple adopted a male child. A few years later, twin boys were born to them. The blood group of the couple is AB positive and O negative. The blood group of the three sons is A positive, B positive, and O positive. The blood group of the adopted son is? [2011]

A married couple adopted a male child. A few years later, twin boys were born to them. The blood group of the couple is AB positive and O negative. The blood group of the three sons is A positive, B positive, and O positive. The blood group of the adopted son is?

O positive
A positive
B positive
Cannot be determined on the basis of the given data

Explanation

Option (a) is correct

A couple with blood groups AB positive and O negative can biologically have children with either A or B blood groups, but not O, since the O group requires both parents to contribute an O allele, which is not possible from an AB parent. Among their three sons—A positive, B positive, and O positive—the child with O positive blood cannot be their biological child. Therefore, the adopted son is the one with O positive blood.

Blood compatibility chart showing donor blood types on the horizontal axis and recipient blood types on the vertical axis, with red blood drop icons indicating compatible transfusions. The chart highlights O- as the universal donor and AB+ as the universal recipient, using a grid layout with labeled blood types and color-coded text for clarity.