Official Answer Key & Detailed Solution
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Correct Answer: Option (A) — O positive
Concept & Option Breakdown
Standard Reference VerifiedGenetics of ABO blood groups: A parent with AB blood group has genotype IAIB, while a parent with O blood group has genotype ii. The possible genotypes of their biological children can only be IAi (Blood group A) or IBi (Blood group B). They cannot biologically produce a child with blood group O (ii). Therefore, the child with blood group O positive must be the adopted son.
An AB parent always passes either allele A or B; hence an AB x O cross can NEVER produce an O offspring. Thus O positive belongs to the adopted child.
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